Enclose | Build: Walls, Facade, Roof 9783035603361, 9783034602075

Table of contents :
Foreword
Contents
Fundamentals
Self-Supporting Envelopes
Non Self-Supporting Envelopes
Roofs
Examples
Appendix
Tables and Information
Standards and Guidelines (Selection)
Associations (Selection)
Manufactures (Selection)
References / Picture Credits
Index

Citation preview

SCA L E ENCLOS E | B UIL D

SCALE

ENCLOSE | BUILD WAL LS, FACADE, ROOF

E D I TO R S

Ale x ander Reichel K erstin Schult z AU T H O R S

E va Maria Herrmann Martin Krammer J örg Sturm Susanne Wart zeck

Birkhäuser Basel

Foreword

Architecture conveys its message via the facade, the building envelope. Houses, urban spaces and landscapes are initially perceived in terms of their overall outward appearance, and only after that in their details. The facade determines the ­appearance of the building, and hence the street space and even the landscape where the building is located. The fifth volume of the SCALE series deals with the facades of buildings, which provide their envelope and depend for their appearance on the construction details. The title Enclose | Build conveys the ambivalence of the subject: the poetry and volatility on the one hand, and the practical necessities of the production process on the other. This volume, together with the volume Support | Materialise, describes all of the building components required for construction and puts them into context, from the design drawing through to technical implementation. It thus makes clear how different design processes influence the idea of construction. Owing to the technical developments of recent decades, facade concepts are increasingly being created almost free of technical restrictions. Furthermore, facades are no longer limited to the vertical plane, but rather envelope the entire building. In consequence, the last chapter but one of this volume deals with the classic structure and principles of roofing, including constructional details. As the public face of a building, its envelope conveys its immediate expression; it bears witness to the historic era of the building and the architect’s approach. Some 150 years ago, Gottfried Semper, a proponent of historicism, postulated that buildings should be cloaked by a facade. He understood buildings to be a fixed volume which should be ‘clothed’, similar to a man with textile garments. Just about fifty years later, the Deutsche Werkbund and the proponents of the International Style that had evolved from the Bauhaus movement turned their back on this attitude; instead they demanded honesty and the proper application of work and materials, with dramatic consequences for the facade. From today’s point of view, the emancipation of architectural form, together with its counter-movement, Post-Modernism, provided the basis of today’s diversity of building envelopes. These combine aesthetics, technology and functionality. They can independently enclose space, determine the character of a space, or even create it. Advances in building technology with respect to building physics, energy efficiency and sustainability raise new issues and provide new solutions for the design of facades. Within this dialogue, we consider it important to discuss the elements that make up envelopes in an authentic and technically correct manner – not just as abstract images, but also in a way that assists the implementation of the respective idea in detail. The diversity of design options is reflected in the diversity of contemporary construction methods. The main part of this volume therefore describes different suspended facade systems and their effects, and presents their principles and characteristics. Following an introductory chapter, we deal with the various envelopes under the categories of self-supporting or non-supporting facade, examining their development and discussing their symbolic, aesthetic and technical possibilities. For the self-supporting envelopes in particular, there are overlaps between the construction methods illustrated in the Support | Materialise volume and the discus-

sion of the principle differences in the construction of a building with non-self-­ supporting envelopes (curtain wall facades). What comes first – the structural system, or the appearance and effect of a building? This ambivalence permeates the entire design process; it has to be faced by all those involved and can only be resolved via an integrative approach to design. Both this and the aforementioned SCALE volume demonstrate that design, material and structure not only depend on each other, but benefit from this interaction: they need this combination to create the desired architectural effect. This also ­depends on the quality of implementation at the different scales – from the outline design stage through to construction detailing. This volume therefore covers the different stages and includes detailed drawings to illustrate the relationship between design principles and construction details. Enclose | Build completes the core of the current SCALE construction series. It would not have been possible without the prolonged and committed involvement of all its authors and contributors, to whom we express our heartfelt gratitude. We would also like to cordially thank the architects and photographers who have provided us with their projects and photographs. Above all, we would like to thank the volume editor, Eva Maria Herrmann, who has pulled the threads together, and Andrea Wiegelmann, who conceived the series and has continuously supported it. We thank Birkhäuser Verlag for its helpful cooperation over a long period of time. We have enjoyed working on these essential architectural issues and their ramifications. We hope you will be inspired by an enthralling read. Darmstadt / Kassel, 31 March 2015 Alexander Reichel, Kerstin Schultz

F UNDAMEN TALS

8

SEL F-SUPP ORTING ENVELOPES

46

NON SEL F-SUPP ORTING ENVELOPES

60

ROOFS

102

E X AMPL ES

128

APPENDIX

154

ENCLOS E | B UIL D Fundamentals

chapter 1

IN T ROD U CTION

10

CULT UR AL CON T E X T – HISTORY

12

PL ACE AND ENVIRONMEN T

14

Climate

16

PRINCIPL ES OF ENCLOSURE

18

AEST HE TIC S, E XPRESSION AND SY MBOLISM

20

COMP OSITION AND PROP ORTION

24

MAT ERIAL AND T E X T URE

26

T Y P OLOGY AND USE

28

ENVELOPE AND CONST RU CTION

30

Protection

36

ECONOM Y AND PROCESS QUALIT Y

38

ECOLOGY AND LIFE CYCL E

40

REF URBISHMEN T, WAST E AND RECYCLING

42

O U T LOOK

44

10  Fundamentals

IN T ROD U CTION

Mankind has been building shelters since time imme­ morial in order to gain protection from the weather, wild animals and enemies. The envelope of these shelters forms the boundary between the outer environment (specific local and climate conditions) and the sheltered interior, which – with as consistent a room temperature and climate as possible – can be used in all of the necessary ways. As demands for people’s general well-being have increased, the requirements have become more complex but the essential, protective function of the building envelope has remained the same. Conversely, the building envelope also has an outward role to play. It enables communication and creates relationships with outdoor space. The term ‘building envelope’ normally refers to the facade, but that is too simplistic. In this book we shall look at the different building elements such as plinth, wall and roof in combination. These can envelope a building like a skin, and are responsible for dealing with all impacts resulting from the environment. Over the course of centuries, many variants have been developed in response to diverse requirements. A decisive influence on the design of the building envelope has always been exerted by the location, its climatic and cultural conditions, and the locally available material. Historically, the availability of materials at a location played a decisive role – one that is now regaining importance due to today’s ecological criteria. Buildings have an effect upon each other depending on how close together they are, forming rural and urban patterns of settlement. It follows that the location of a building is paramount in importance and has a fundamental influence on the shape and design of the envelope. While

nomads developed element-based envelopes in the form of tent-like constructions for flexible, temporary use, ­settled populations developed solid forms of enclosure which were place-specific and designed for durability. Likewise, the location of a building involves both cultural and historic influences. For example, depending on the cultural context and the era, the connection or separation of public and private space can become visible and thereby reflect the social structures of the society. To this day the envelope of a building is an expression of the social status and position of its users. In the case of public buildings with a representational function, the facade will always reveal the attitude to society of those who built it; it has always been used to express wealth, in­ fluence and power. The function of a building has a significant effect on the construction and design of the ­facade. The close interplay between facade, internal ­arrangement and construction determines its composition, transparency and openings. While up into the twentieth century the building envelope was normally not just a space enclosure but also part of the loadbearing structure, the dematerialisation of the once structural wall to create the suspended facade, which can fulfil structural and symbolic functions, has opened up a range of aesthetic and functional options. Whereas solid structural envelopes impose limits on the design of openings (facade with windows), the conti­nuous development of new building materials is enabling a separation of the envelope from the loadbearing ­structure, providing greater flexibility and freedom in the ­facade ­design. The loadbearing elements of a building can either be concealed by the envelope, be visible in ­interaction

1 Tent structure in Arabia In the arid zones of Persia and ­Arabia where timber is scarce, tent poles were covered with highstrength fabrics in order to create large, well ventilated envelopes that provided protection from the sun. The height of these structures was determined by the length of poles available, the size and strength of the cloth and the process of putting up the structure, which remained unstable until it was tied down. 2 Borie in the south of France The corbelled vaulting consists of small, unworked flat stones and has been used in rural areas up to ­modern times. These stone houses have a pointed roof and are built without cement and mortar. The building technique, with its small components, is typical of a manual process. 1

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INTRODUCTION  11

with the envelope, or become the main design theme. The enclosing envelope is directly related to the type of use, the loadbearing structure and the building services ­installations. Constant feedback relating to function, construction and expression is necessary to produce a well-integrated overall design. A building envelope is not just about the building surface. It fulfils a multitude of functions. The quality of an envelope can only be assessed in the overall context of functional, structural, stylistic, ecological and sociological criteria. Depending on the concept, it will have not only a protective function but also those of structural support, climate control, lighting and communication with the surroundings. The expression and form of a facade result from the multiple requirements the building envelope has to fulfil. For example, the design of a facade may be determined by use, function, or construction respectively; alternatively, a facade may have a purely sculptural and expressive ­intent. It may represent the function of a building in a symbolic or iconic way to the outside, or fulfil a specific purpose as a landmark (e.g. a lighthouse). The interplay of these factors determines the appearance and overall ­impression of the building. One contemporary development is to see the envelope as an active system within a sustainable energy concept. Depending on the approach and possibilities, this may take a variety of forms, ranging from simple folding shutters in front of windows for shade, to glass facades with controlled ventilation openings, daylight control systems or integrated photovoltaic panels for the generation of energy.

3 The Curtain Wall House, Tokyo, 1997, Shigeru Ban The Curtain Wall House is sym­ bolic of the emancipation of the ­envelope from the loadbearing structure. Weather protection is ­afforded by a textile curtain which, when open, eliminates the boundary between the interior and the ­exterior. The private space becomes public, and the public space becomes part of the private sphere. 4 The Opera House, Oslo, 2008, Snøhetta The plinth, walls and roof of the building merge seamlessly to create a walk-on roof landscape. The additional public urban space thus created adds to the amenity value.

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Increasingly the ecological assessment of a facade not only focuses on the energy demand or energy gain during its service life, but is extended to include the eco-balance over the complete life cycles of its constituent parts – from the production of the raw material to the disposal of the envelope. This highlights the connection between economic efficiency and ecology. The overall assessment of the life cycle can reveal important information about the cost efficiency of a facade during its service life, apart from the cost of construction. This includes the ­expenses of cleaning, maintenance, renovation and renewing materials. It follows that building envelopes should be considered not in isolation, but as complex elements that are integrated into the design process. This increases the ­demands on the design team and the design and implementation processes. This book complements the Scale volume Support | ­Materialise in addressing the subjects of enclosure and building with a focus on the fundamental systems and principles of the loadbearing structure and the facade – from the foundations to the roof. It aims to illustrate the breadth of options in designing envelopes, as well as their limitations, and to develop an understanding of their technical implementation. This publication is intended to encourage solution-oriented thinking, involving constant reference to context, typology and construction, rather than strict obedience to a given design principle.

12  Fundamentals

CU LT UR AL CON T E X T – HISTORY

Original architectural space fulfils the simplest functional requirements – those associated with providing protection – with the use of locally available materials. Gottfried Semper, writing in the middle of the nineteenth century, developed a theory of the facade which he ­derived from the lightweight but effective construction of nomadic tents – which are still in use today with their system of a separate loadbearing structure and a protective envelope, even in extreme climatic conditions. As in the world of fashion the garment envelopes the space of human existence. Rather than the functional technology of construction, Semper emphasised the symbolic and cultural criteria for the suitability of the architecture. While early buildings were designed along purely functional lines in response to a given situation, over the course of history the concept of buildings as accommodation evolved from one of being purely protective into the discipline of architectural design. The collapsible, enveloping structures of migrating peoples were replaced by buildings designed for permanence. Just as in clothing there are many variations of colour, weaving patterns and textures, so too the positioning of openings, the arrangement of structural elements – such as arches and columns – of friezes, paintings and sculptural, figurative elements developed as independent forms of expression. The term ‘facade’ derives from the Latin ‘facies’ (face), which was used in antiquity to describe the publicly visible side of a building – especially of prestigious buildings (sacral as well as secular). A structure built by the hand of Man symbolises the interaction between the individual, the outside space and society. This encompasses the climate and topographic contexts on one hand, the reflection of societal forms, political intent, religious provenance and ethnic grouping on the other, and even the availability of local resources. A building serves as a store of information, and is at the same time a witness of different epochs. Since time immemorial, people have availed themselves of the power of expression inherent in built forms. The pyramids are the mighty enclosure of a pharaoh who thus manifested his power and his connection with the heavens to his contemporaries and for posterity. While the early democratic structures of the Greeks and Romans resulted in residential buildings having private, introverted inner courtyards, public temples were designed to be all the more ostentatious. From the Middle Ages onwards, as a society of citizens and tradesmen developed, the facades of secular buildings were also increasingly decorated for representational purposes. Openings acquired special importance. They served as a filter between the exterior and the interior that could be opened to a greater or lesser degree.

Even though the size of windows in residential buildings was limited for a long time, the openings themselves were often elaborately designed. Coloured or moulded surrounds emphasised their importance in the facade. In Gothic architecture, parts of the external wall were relieved of their structural functions for the first time, by elements such as columns, flying buttresses, ribs or piers. In place of the masonry came large windows intersected by tracery. While in the Gothic period the envelope consisted chiefly of the supporting structure, in the Renaissance the facade became separated from the building and was understood as a separate design element. In the time of industrialisation, from the middle of the nineteenth century, new materials and construction methods (such as the skeleton construction method) and new building types (such as industrial buildings and warehouses) brought about a fundamental change. Large glazed facade openings become possible and heralded the transition to the first all-glass facades. With the ­onset of the Modern age, the influence of the building structure on the enclosing envelope was reduced and the envelope became an independent component of the design. The separation of the loadbearing structure from the envelope can go as far as completely dissolving their original connection. In Post-Modernism, an architectural style from the 1960s to 1980s, facades were placed as backdrops or stage sets for the space in front of a building and in this way re-applied the principles of the Renaissance. In later developments, some facades became fully independent of the building and developed into standalone, sculptural forms with their own – sometimes iconographic – meaning. The discrepancy between preservation and creative development is considerable. Freezing a supposedly ideal state of affairs can lead to ‘pattern book’ architecture and regression, just as disregard for the cultural context gives birth to ‘foreign bodies’ that strain to create an effect at all costs rather than integrating into an urban context. Today too, the interface between interior and exterior reflects the cultural context in a reference to the social structures of the society and the place where they have developed, and in the sense – propagated by Modernism – that openness, transparency and design are to be understood as expressions of democratic society. In the future, the functionality of facades will be extended even further. Technical progress has made it possible for facades and roofs to absorb and process energy, to dispose of dirt, to provide acoustic insulation and to transmit information. At a highly technical level, the envelope performs tasks which are also expressed in its appearance – be it imperceptibly or conspicuously.

1 Traditional housing in Cameroon, consisting of pressed, sun-dried clay in the form of a conical shell. 2 Stralsund Town Hall, 1278: This magnificent facade has a strong representative intent, being higher than the three-storey town hall that it fronts. 3 Togu-do, Kyoto, 15th century: The Togu-do is built in the Shoin ­architectural style. Built as a private residence and subsequently used as a temple, the Togu-do contains a room for the tea ceremony, which became the archetype of all later tea rooms (chashitsu) in ­Japan. 4 Palace on the Grand Canal, ­Venice, early 15th century: The ­elegant palace is a typical example of the special style of the Venetian ­Gothic. 5 Grote Markt, Antwerp, 16th ­century: The status of the city of Antwerp in the 15th and 16th ­centuries, as one of Europe’s foremost commercial and cultural ­centres, is demonstrated by the luxuriously designed guild halls and citizens’ houses. 6 The Majolica House, Vienna, 1898, Otto Wagner: Inspired by Gottfried Semper’s theory of ‘dressing’, Otto Wagner uses facade cladding with thin, precious materials – here in the form of tiles with floral motifs – in order to give the building an appearance that is independent of the construction. 7 The Fagus factory, Alfeld, 1911–1913, Walter Gropius and Adolf Meyer: In this building, glass is used as enclosing element, in­ dependent of the loadbearing structure. The corner is built without a column, thus emphasising the lightweight character of the transparent envelope. 8 The Seagram Building, New York, 1957, Mies van der Rohe: The bronze-coloured tower block is deemed to be the prime example of the ‘skin and bones’ architecture of Mies van der Rohe and still serves as an ideal prototype for skyscrapers. The facade is subdivided using slender bronze profiles, the spacing of which is reduced ­towards the building corners in ­order to emphasise the verticality of the tower block.

CULTURAL CONTEXT – HISTORY  13

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14  Fundamentals

PL ACE AND ENVIRONMEN T

The individual connection with the environment, the historic, cultural, climatic and material conditions of a place require careful analysis. Only dialogue with the place ­itself makes the quality of architecture visible and tangible – conversely, a misunderstood reference to the place will have an effect on the popular acceptance of a building and its sense of belonging. The issues are not only those of urban space, landscape and topography, but also those of climate conditions and local resources – which influence the use of energy and technology – in addition to building control requirements. For example, glass facades either mirror the surroundings – be they urban or rural – or allow a view into the building, depending on the angle of vision, reflection and time of day. It is possible to emphasise transparency and views into the building in order to let the building meld  1 into the townscape or a country landscape. Buildings are in a dialogue with their surroundings. They can be designed in keeping with the landscape or surroundings or in deliberate contrast to them. Owing to the material used, the turf roof houses of Iceland blend well with the landscape and replicate the hilly topography of the surroundings. On the other hand, envelopes can be integrated in a cultural context while contrasting completely with their surroundings, either by complementary colouring or an unusual use of a traditional material.  2

In today’s globalised world, identity and tradition are gaining new significance. Available regional resources, knowhow relating to materials, old and new processing methods and economic means of transport are becoming increasingly important. Social acknowledgement is also reflected in the degree of self-confidence that is evident in architecture. Tra­

ditional construction methods and modern vocabularies of form complement each other in a meaningful way.  3 A place is not only defined by the orientation of a building to account for the site boundaries and the cardinal directions, but also by the characteristics of the site itself, be it level, sloping, dipped, or even partly covered by water. The conditions on a given site can be accommodated in the design in a number of different ways. The landscape may be one of rolling hills or ragged rock; rounded or angular elements may dominate; the surroundings may be matte or feature a smooth, shiny surface, while the colours of the landscape may change over the course of the seasons. The building, in turn, may stand out from its surroundings or reflect them; it may continue the terrain or completely merge with it. The existing context can even be exploited to generate the design. In areas where buildings are highly exposed to the weather, a plinth is often used as transition between the ground surface and the building itself. In addition to its protective function, the plinth – with its material, surface finish and colour – can also serve as a formative element in the design.  4 On the other hand, the volume of a building with a fixed schedule of accommodation can be visually reduced by placing the required space partly or wholly under the natural contours of the terrain.  5, 6 Where this is required, new buildings can be integrated inconspicuously in landscape areas worth protecting or in established urban areas. Alternatively, they can enhance the surroundings if judiciously placed in a prominent position. In this case, the local topography makes additional demands on the material and construction. The design of a freestanding, exposed building must pay more attention to watertightness, airtightness and durability than a one that is sheltered by landscape features or other ­buildings.

1 Tower block ensemble, Ulmenstrasse, Frankfurt am Main, 2009, Max Dudler: Two existing tower blocks were revitalised with a contemporary element facade, which is nevertheless in keeping with the Wilhelminian buildings in the neighbourhood, owing to the proportion of openings and the material ­chosen. 2 The Ecumenical Forum, ­Hamburg, 2012, Wandel Hoefer Lorch: Typical for the location, brick is used as the face material of the back-ventilated suspended facade, which nevertheless reinterprets the local style with its shape and colour scheme.

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3 The Floating House, Ontario, 2008, MOS Architects: The varied properties of timber as a construction material – including the fact that it floats – were used in the ­construction of a holiday home; the building was assembled on land using prefabricated timber elements which were later installed on a floating pontoon at an island in the lake.

PLACE AND ENVIRONMENT  15

4 Timber houses in the Valais This specific, local style of building is a direct response to the location (climate and topography) and materials (timber and stone). The natural stone plinth is used to level the terrain; it also protects against snow and moisture and serves as the foundation for the timber structure. The vertical arrangement of functions – plinth, stables, living space – and hence the use of natural ven­ tilation and heat, determines the particular style of houses in the ­region. 5 Visitor centre at the Hercules monument, Kassel, 2011, Staab Architects: The form is the result of the location (topography, and view of the Hercules monument). The building follows the natural ­gradient of the terrain and, by cleverly integrating various functions, manages the differences in level without creating excessive volume on the slope.

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6 Extension to the Städel ­Museum, Frankfurt am Main, 2012, Schneider + Schumacher: The special feature of this locality (open space in the inner city) is retained by placing the building underground. The underground structure provides the floor space required for the exhibitions, which receive ­filtered light from above while ­allowing use of the roof area as a public open space.

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16  Fundamentals

CLIMAT E

Traditionally, the design of facades and roofs was and still is primarily determined by the local climate. The construction of walls and roofs developed in tandem with the respective trade skills. Materials and construction methods were used in ways that kept costs low while ensuring the longest possible service life. The shape of the building – its volume, roof pitch and eaves overhang – was a direct response to the respective weather conditions. From time immemorial the climate has been the dominating factor in the design of buildings that evolved from inherited experience. Also referred to as autochthonous building, this approach employs the naturally available ­local resources in a way that is appropriate for the climate and the use. In regions exposed to heavy snowfall, shallow-pitched roofs with natural stone covering (additional mass to counteract the risk of the roof lifting off and to stop snow from sliding off the roof so that its insulating properties can be used) and large eaves overhangs are common. Conversely, steeply pitched roofs reaching down close to the ground can better withstand rain and the horizontal forces generated by strong wind.  1 In hot climate zones with little precipitation, monopitch or flat roofs usually predominate. In these areas, solar irradiation into the building is minimised by large canopies, small atria and the dense juxtaposition of buildings. Thick, solid walls with small window openings provide storage mass with a phase shift, which keeps the building cool during the day and warm during the night.  2 Large eaves overhangs form intermediate climatic zones and prevent overheating in summer. Numerous requirements, which can be met with more or less advanced technical and functional input, continue to influence the development and execution of the envelope. Local weather conditions on the outside should not adversely affect the cosiness and comfort of the interior. This applies not only in regions with extreme day-to-night and summer-to-winter fluctuations, or in sub-polar and -tropical zones, but also in temperate zones, as in central Europe, where the climate is subject to pronounced regional differences. Every place has a specific climate which is determined by its topography and situation. Consideration should be given not only to the differences between mountainous, inland and coastal regions, but also the differences in the microclimate, such as those between urban and rural areas and those within an urban environment. It follows that a detailed analysis of regional climate data, which are summarised in the thermal insulation standards and are obtainable in greater detail from the databases of regional weather stations, is an essential prerequisite for the design of the building envelope.  SCALE, vol. 2, Heat | Cool

While it is not possible to change the exterior conditions imposed by the choice of location, the type and functionality of the facade and roof can be influenced by the design. Infrastructure and industrial buildings are naturally subject to different comfort criteria than residential, cultural and sports buildings.  p. 28, Typology and Use In addition to the general requirements for thermal comfort in the interior, the facade has to fulfil additional functions. Acoustic requirements, such as insulation from the noise of traffic and machinery, have to be taken into ­account, as have the hygienic requirements for air quality, ventilation and the prevention of air pollution from the outside. The need to reduce glare and contrast while meeting requirements for sufficient daylight influences the type and size of openings and the choice of building  components for solar screening and light control.  SCALE, vol. 1, Open | Close Energy-efficient use of the ­facade, including energy generation and control, introduces greater complexity into the design of the envelope. The better the thermal properties of the materials of the envelope are, the less energy is required in summer for cooling and in winter for heating. Due to globalisation, the materials and construction methods used in different countries are becoming ever more similar. With the beginning of industrialisation, new technologies and means of transport made construction less dependent on local materials, and design more ­independent of the local weather conditions. However, current sustainability studies have highlighted the opportunity to conserve energy and resources by using regional materials and building types to protect against heat and  3 cold. What are the local climate conditions and how should they be dealt with? How much energy input can be expected from sunlight, and how is it possible to integrate solar screening in the design while making use of the potential energy gain? Instead of relying solely on ever more sophisticated technology to meet the increasing demands made of building envelopes, the architectural ­designs of the future will have to exploit appropriate ­materials and forms in dealing with the prevailing climate conditions. The design and implementation of building envelopes must be based on a comprehensive assessment of all the parameters and their interaction. All these factors relating to a locality and its cultural ­basis indicate why, in architecture, each design task must be fully appraised anew. Similarly, tried and trusted typological, technical, or conceptual solutions should not be transferred from one project to another without close ­examination. Different places and different times will ­always give rise to very specific, original solutions.

CLIMATE  17

1 Traditional farmhouse in the Black Forest The shape and overhang of the roof provide protection from rain and snow as well as plenty of space for the storage of hay, which also insulates the interior in winter, thereby contributing to the occupants’ ­comfort.

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2 Traditional building structure in a desert climate Clay is an available local resource and is used in solid construction. By zoning the layout, protected areas are created (in the shade or close to the relatively cool ground). The knowledge of physical phenomena (cold air sinks) allows the utilisation of natural cooling resources by ­creating an air draught, which is caused by the small temperature differences in the shaded parts of a building. This has led to a distinct type of structure known as a ‘wind tower’. 2

3 Office building 2226, Lustenau, 2013, Baumschlager Eberle: ­Experimental office building without heating. The building has ventilation and cooling (by air), which is actively controlled and utilised. The material used is brick which, with an external wall thickness of 76 cm and a low proportion of openings to solid wall, is used as storage mass. This makes it possible, using only internal heat sources such as lighting, equipment and users, to ­retain enough heat in the building to ensure thermal comfort. In this way the traditional construction feature of thick masonry walls has been modified as the basis of an energy-conserving concept using control technology (air).

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18  Fundamentals

PRINCIPL ES OF ENCLOSURE

Facades vividly express the interaction between construction and design, functionality and aesthetics. The loadbearing function of an envelope cannot be considered in isolation, but represents an integrated system which takes factors such as environmental context, climate and use into account. The more functions an exterior envelope has to fulfil – such as structural support, protection against the weather – and the more it is intended to express the purpose and aesthetics of the building, the more complex is the design task. Conversely, many more design options are available when the facade does not have to meet structural and functional requirements. In this context, an understanding of the unity of technology and aesthetics is the prerequisite for a good, holistically accomplished design. In the design process, the focus is on the structural system of the secondary  structure, as well as on the materials and the desired ­appearance. Both the surface finish (from smooth to ­textured) and the design of the form (composition, ­pro­portion of elements and joints) have to be taken into ­account to the same degree as technical feasibility (in the form of production conditions, prefabrication processes and installation). At the design stage, it is ne­ cessary to ­establish how the material relates to the ­en­vi­ronment  p. 40, Ecology and Life Cycle, and also how cost efficiency, material selection and construction are  p. 38, Economy and Process Quality The require­affected. ments for a new building are different to those for a ­conversion, a rehab (usually strengthening an existing structure) or a refurbishment, which are often linked with the preservation of historic buildings and represent more complex tasks with respect to the unity of aes­thetics and technology. The different components of a building ­envelope – plinth, wall, openings, roof – have to fulfil different functions depending on their respective ­positions. The plinth is the interface between the building and the ground, and can either be perceived as an independent element (e.g. in a different material or colour) or be integrated into the envelope. In addition to its functional ­requirements – transmission and distribution of loads from the loadbearing structure and envelope, protection against water and/or external influences and intruders, compensation for differences in the level of the terrain etc. – a plinth can also make a formal statement. A solid plinth with the height of a full storey may appear forbidding, whereas an open and transparent ground-level area

has an inviting feel. On the other hand, the plinth often combines different types of enclosure. In buildings where both commercial and residential uses have to be accommodated, a different style of plinth can help with the orientation between public and private areas. Topographic and climatic conditions determine the choice of plinth material – either based on and rising out of the ground, or detached in a different plane. Depending on its surroundings, a building can even be designed without a plinth – that is to say, a plinth without any distinct appearance – in favour of a more homogeneous ­envelope. When the facade serves only as a thermal enclosure of the interior, the separation of the loadbearing function from the enclosing function  SCALE, vol. 3, Support | ­Materialise allows much more freedom in the design – be it in the visual expression of structural elements or the application of a more abstract design, be it showing the true nature of the material or mystifying it. With the transformation of the flat wall (solid construction) into a transparent enclosure of space with a system of beams and columns (skeleton construction) and cladding, the classic image of the solid wall and its visually expressed functions changes in favour of a more autonomous envelope. While in solid construction the openings are largely determined by the construction grid for structural reasons, the position of openings in skeleton construction is not determined by any particular order or geometry.  SCALE, vol. 1, Open | Close

The facade and the roof together form the visible en­ velope of a building. For this reason, the design of the ­envelope is ruled by universal principles. The com­ position  of envelopes ranges from clearly distinguishable ­elements – plinth, wall, roof – to seamless, tent-like ­designs. The envelope will always follow the shape of the building. Its appearance can be changed to suit the design approach, the context, the topography and the type of construction. For example, we are familiar with the principle of filigree facades in the Venetian Gothic, just as we know it from the Belgian art nouveau style, from historic timber construction and from modern concrete facades. The basic principles are illustrated by the adjacent drawings and on the following pages.

PRINCIPLES OF ENCLOSURE  19

1 Position of envelope a Construction elements: plinth, wall, opening, roof Separation of building components, solid construction > skeleton ­construction b Building volume + cold roof c Building volume + warm roof (overhang) 1a d Skeleton structure + envelope (seamless) or loadbearing structure + envelope

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2 Appearance / form a Volume with roof overhang b Smooth / homogeneous building volume c Projections and recesses d Concealed elements

3 Design of envelope a Solid, enclosed b Slender, transparent c Overlays, filter between solid and open d Position of openings in the ­envelope

4 Context a Free-standing b Built adjoining an existing ­building c Integrated with an existing ­building d Extra volume on an existing building

5 Topography / climate a Buried b Transition zone between building and envelope c Integration of foundations and plinth d Integration into an existing ­envelope with a new thermal ­envelope – external envelope – ­internal envelope

20  Fundamentals

AEST HE TIC S, E XPRESSION AND SY MBOLISM

The envelope of a building is sometimes referred to as its face. It provides the building with a specific e ­ xpression. In addition to the functional requirements – to protect, to keep warm and cool, ideally via specially generated and/or stored energy – a facade will always have a formal expression and a symbolic significance. The enclosing envelope is the first thing that is perceived from the ­outside. ‘Each building, each facade is a public affair. The facade belongs to everyone, only what is behind it belongs to those who have to live with it. And for this reason, it is also clear that facades must not be a matter of cos­ metics.’ Manfred Sack, an architectural journalist, has ­defined the architect’s task thus. The symbolic message of an envelope must not be used for purely decorative purposes and hence be misappropriated; instead, the shape and materials should be used to make a statement about the building’s use and context, social structure and attitude. The design is not just perceived as the sum of elements and forms, but imparts symbolic expression and orientation in multi-faceted ways. Facades have always conveyed a message. The sacral and secular images in the form of ceramic tile screens which adorn the public faces of buildings in Porto and Lisbon can hardly be bettered in terms of opulence and wealth of motif  1 as they assert society’s claim to ­exercise power and convey its values. This early form of ‘media facade’ experienced a revival with Antoni Gaudí’s interpretation of the legend of St. George on ceramic tiles applied to the facade of Casa Batlló.  2 Its latest incarnation is the printed glass facade, as used in the

new Ricola factory building by architects Herzog & de ­Meuron. These three-dimensional compositions contribute to the expression of the building and inspire a new world of ideas; the building can function as a symbol and convey an extended message. Sacral buildings often consist of lofty, vertical structures, which allude to a higher order of  existence. Public buildings with monumental rows of ­columns are intended to express the power of the ruler or the state. Ostentatious palaces symbolise a claim to authority, and today evoke fantasies of the world of times gone by.  5 The form, surface texture, materials and colour  4, 6 of a facade are the design characteristics that determine the external appearance of a building, and can be used to reinforce the symbolism. While retaining the volume, the facade can be structured and given rhythm using colour, ornament or changes of material. A smooth facade,  7, 8 on the other hand, can seem to have any scale. Depending on the weather and the fall of light, the envelope can take on different appearances and can exploit changeable conditions to generate nuances. For example, the Centre for the Development of Local Alabaster in Teruel appears stone-faced and forbidding during the day, but at dusk it conveys an ethereal, textile feel due to the wafer-thin stone envelope.

1 Azulejo on the outside facade of a church, Porto, from the 16th century: Mosaic consisting of fired ceramic tiles, mostly square, with colourful painted decorations. A characteristic feature of the townscape on public monuments and buildings, house facades and churches, as well as on internal walls for the purpose of decoration, often composed as large-scale ­pictorial murals. 2 Casa Batlló, Barcelona, 1877, Antoni Gaudí: The colourful facade represents the legend of Saint George, the patron saint of ­Catalonia (locally called Sant Jordi); the roof represents the scales of the dragon fought by Saint George; the cross on the roof is his lance. The forged iron balconies represent skulls and the gallery on the first floor the mouth of the dragon.

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AESTHETICS, EXPRESSION AND SYMBOLISM  21

3 Notre-Dame, Paris, ­1163–1345: The cathedral is one of the earliest Gothic buildings in France. The well-balanced vertical and horizontal structuring of the west facade, as well as the centrally placed rose window, served as an example for many Gothic cathedrals. 4 The Schröder House, Utrecht, 1924, Gerrit Rietveld: The house is one of the most important buildings of the De Stijl movement. The cubic shape and the use of the ­primary colours (red, blue and yellow) in combination with white, black and grey is characteristic of the house’s abstract vocabulary of form. 5 Hawa Mahal, Jaipur, 1799: The Palace of the Winds is part of a prestigious palace precinct of the Maharajas of Jaipur. It features a facade with 953 beautiful openings, with a sophisticated design providing the necessary ventilation. They also allowed the Maharaja’s court ladies to look out without ­being seen themselves. 6 The Millard House, Pasadena, 1923, Frank Lloyd Wright: The house is an experiment in using economical concrete blocks, which are enhanced by ornamentation, thereby also expressing the ver­ satility and beauty of concrete. Decoration and function – outside and inside – demonstrate a new commitment to the material, giving the building a modern appearance for its time.

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7 The Shirokane House, Tokyo, 2013, Kiyotoshi Mori & Natsuko Kawamura, MDS: The decision to design this residence without windows is a reaction to the typically very confined situation in Tokyo and the consequently high density of development. The envelope is closed to the surroundings; daylight reaches the interior via rooflights and a roof terrace. 8 Centre for the Development of Local Alabaster, Teruel, 2011, ­Magén Architects: The centre ­focuses on the export and marketing of alabaster, which is quarried in the region. The opaque and ­translucent surfaces, and the many different forms of the material, function as exhibits. At night, the thinly cut facade elements give the building envelope a translucent appearance.

22  Fundamentals

Symbolism 1 National Congress, Brasília, 1957–1964, Oscar Niemeyer: The building reflects the political structure of the country in an impressive way – while the Senate convenes beneath a concave dome, the House of Representatives resembles a shallow dish. Both parts of the building are connected via the ground floor and the development includes two office tower blocks.

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2 Nakagin Capsule Tower, Tokyo, 1972, Kisho Kurokawa: The building is an icon of the Metabolist movement. The standardised housing units are suspended from the core and flexibly connected with each other. The principle of modular composition was also followed in the design of entire townships. Corporate architecture 3 The Chrysler Building, New York, 1930, William Van Alen: The building was designed in the Art Déco style. The upper part of the facade features gargoyles in stainless steel that are reminiscent of the wheel covers, wings and bonnets of the vehicle brand; in addition, Chrysler wheel covers have been used to decorate the facade. 4 Best Store facade, 1970, SITE: The Post-Modern style plays with traditional concepts of the classical facade, and in this variant becomes architectural pop art.

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5 BMW Munich, 1972, Karl Schwanzer: The succinct shape of the four cylinders reflects the desire of the Bavarian automotive ­corporation to have a directly symbolic landmark; at the same time, it derives from a new type of internal layout and the suspended construction from a central core. Iconography 6 The Sydney Opera House, 1973, Jørn Utzon: The geometric shape – which accommodates the stages and concert halls with a gesture that is both protective and presentational – is a very memorable sculpture. It became a worldwide icon and a landmark in Sydney. 7 The Guggenheim Museum, ­Bilbao, 1997, Frank O. Gehry: The solid, cuboid building parts are ­assembled like a seemingly haphazard collage, with the external form reflecting the arrangement of the art objects in the flowing interior.

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AESTHETICS, EXPRESSION AND SYMBOLISM  23

Tradition and high-tech 8 The Institut du Monde Arabe, Paris, 1987, Jean Nouvel: Traditional Arab ornamentation has been ­reinterpreted and given a new function in a contemporary architectural language. 9 The Centre Pompidou, Paris, 1977, Renzo Piano & Richard ­Rogers: The technical aesthetic of high-tech architecture was taken as the main focus of the design. The facade has become a multifunctional part of the building, providing access and accommodating the services installations, thus leaving the interior space with maximum flexibility. 8

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In his government buildings in Brasilia, the capital city built from scratch between 1957 and 1964, Oscar ­Niemeyer succeeded well in combining an aesthetic ­effect with a symbolic claim.  1 As a counter-gesture to an architecture of power, the free sculptural shapes come across as an impressive expression of democratic representation. Architectural history has many instances where a certain design trend gave birth to a style. With the ‘detachment’ of the envelope from the loadbearing structure at the ­beginning of the twentieth century, the focus turned to the technical and material quality of the facade and its texture. There is a fine line between the necessary function and abstract aesthetics. Subsequent decades saw examples of both extremes. This is evidenced by two styles which developed in parallel and represent two ­opposite approaches to design: Postmodernism and the style of architecture referred to as High-tech. While Postmodernism, with its playful and sometimes witty handling of building elements and formal details, tried to escape the aesthetic dictate of functionalism and rationalism  4, the High-tech style of architecture relied on the pattern language offered by the technical elements of construction. The idea is not based on an emphasis on innovative technology, but on the expression of a technology-based aesthetic. A typical example is the Centre Pompidou as a ‘culture machine’ in the historic centre of Paris, the exterior appearance of which is shaped by the structural elements as well as the service installations and access elements. The interior is kept clear of columns and thereby offers maximum flexibility of use.  9 Some buildings can be very clearly identified by their exterior shape, so that the envelope and hence the facade acquire iconographic importance.

The identification of the public with ‘their’ building can give rise to symbolic nicknames such as ‘The Oyster’used for Sydney Opera House  6 with its spectacular shelllike structure surrounded by water on three sides. The  8 is a facade of the Institut du Monde Arabe in Paris symbol of cultural provenance and a metaphor for the function of the building. The facade with its ornamental vocabulary of form is both a technical building component – the facade elements control the incoming daylight in a similar way to the iris of a camera lens – as well as a reminder of traditional Arab construction elements. Another landmark of iconographic architecture is what has become known as the BMW Vierzylinder (four cylinders). Built in 1972 as the car manufacturer’s head office and landmark, this design – which for the time was innovative – portrays the engine as a symbol and also presents the company as a brand.  5 This building is thus a precursor of corporate architecture, which today is increasingly used for the purpose of marketing the identity of a company. The fact that architecture designed as a landmark can have far-reaching consequences is sometimes referred to as the Bilbao-Effect, which in a positive sense refers to the commercially successful development of tourism in a city area due to an iconographic building. The way a building looks is not just an artistic concern, but is to a certain extent also important from the point of view of economy and ecology. The design of modern building envelopes is more than ever determined by the contemporary use of materials in accordance with their local availability, the honesty of form and composition, the aging ability of materials and the quality of the execution.

24  Fundamentals

COMP OSITION AND PROP ORTION

‘I have never yet designed a facade’ commented the American architect John Lautner who, in the 1960s, built mostly organic residences in which the interior merges seamlessly with the exterior. With regard to the complex constructions and varied forms found in contemporary architecture, this understanding of a building envelope and space seems comprehensible. When looked at closely, however, geometry, areas, lines and volumes are not just empty design features, but result from specific construction elements and how they are joined together. The determination of dimensions, joints, edges, volumes and openings as part of the design directly affects building construction and conversely, the construction requirements of the loadbearing structure feed back into the process of conceptual design. The result is a design dialogue between the abstract determination of form and the validation of its actual implementation. The feel of a facade – and hence the intended effect of the architecture – is generated primarily through the proportions of the volume. The tenets of proportion, which aim for order among the elements making up a design, go back to Ancient Greece and are still valid today. Common to all of them is an appropriate relationship between horizontal and vertical dimensions, with regard to the type of building, its use and the user’s comfort. Independently of the geometry of the building, the overall impression is also influenced by the type and texture of the building materials. A flat finish, such as plaster or a paint coating, generates homogeneity and restraint, whereas a classic frame-based facade – a non-loadbearing glass facade with large panels and its own secondary structure – will always create linear order with its profiles and will therefore determine the appearance of the facade. The composition of facade elements, their size and hence their aesthetic expression are influenced by standardised production processes and the feasibility of onsite ­assembly or delivery as prefabricated units.  p. 26,

Flat building elements appear in numerous forms in a ­facade. They may be straight, curved, textured, smooth, or perforated and, depending on the material, may be used in different sizes and with different colours and finishes. Large elements usually appear like panels owing to their joints, whereas small elements are more likely to come across as a homogeneous structure, in much the same way as pixels do. Similarly, panes of glass can appear as flat areas, either ‘closed’ as a result of the reflection of their surroundings or as ‘outlooks’ in a ‘closed’ wall. Lines appear where flat areas are joined. The edges of volumes and openings also form lines, which form the building’s contours. The lines can be made visible as edges, joint profiles, or transitions between colours. The intersection and superimposition of lines in facades can become the determining design characteristic and may need very careful planning. Bodies are those elements in a building envelope that have depth as well as planarity. The interplay between geometry and construction – and the material – determines whether a facade is perceived more as consisting of individual areas or as a homogeneous body. In buildings, the surfaces of which are constructed in a continuous manner without joints and consisting of one material, the sculptural nature of the body can be particularly prominent.

Material and Texture

vol. 1, Open | Close

OPENINGS In addition to their primary task of admitting light to the interior of the building, openings in architecture are an important design tool, even though they can only be called geometric elements with a degree of reservation. They connect the interior with the exterior and interact with other design and lighting elements. The forms that they take are closely related to the socio-cultural significance of windows and doors as an interface between public space and the sheltered, private sphere.  SCALE,

Historic and regional theories of proportion, amongst others: – The golden section: The golden section is based on the mathematics of classical ­antiquity and results from the geometric definition of line segments to each other in a certain algebraic equation: a / b = b / a + b. – Orders of columns: The most important system of proportion in classical antiquity, which was revived in the ­Renaissance. – The theories of the Renaissance: Andrea Palladio: Quattro libri dell’architettura (Four books on architecture), Venice 1570 – Leonardo da Vinci’s ‘Vitruvian Man’ illustrates the proportions of the human body. – Modulor: A proportional system developed by Le Corbusier between 1942 and 1955. – The Ken: Japanese unit of measure based on the traditional tatami mat module and used as the basis of construction, choice of material and composition.

1 The cube a Closed / open b Cube on a receding plinth / cube with receding upper floor c Cubes offset from each other, eventually leading to free-form ­design

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COMPOSITION AND PROPORTION  25

2 Design – construction – effect a Homogeneous surfaces e.g. render / paint coating, also ­masonry or wood shingles b Subdivision of areas into elements; dimensions depend on the material, e.g. glass panes, ­panels, boards c Vertical subdivision wood, glass

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d Horizontal subdivision wood, metal, fibre-board e Subdivision imposed by the ­panel format, various formats f Proportion and jointing as a ­result of changes in format and ­material g Prestigious facade, placed in front of the actual building to create a certain impression h Perspective, use of perspective to create an ­illusion and distract from the actual dimensions i Free form, folding, disruption of proportions and ­composition

3 Openings – proportion – ­composition a Facade with openings b Hybrid facade with individual windows and large glazed area c Fully glazed facade, separate from the loadbearing structure 4 a b c

Position of opening Flush with the surface Recessed with reveals Surface-mounted

5 Composition a Without grid b Not following the grid lines c Grid camouflaged through the interplay of transparent and translucent areas, or through changes of material

26  Fundamentals

MAT ERIAL AND T E X T URE

Materials are perceived with all the senses. For this reason their use in the design of a facade is not just based on their structural and functional properties, but also – and primarily so – on their aesthetic and perceptual ­effect. Even though the surfaces of buildings are rarely touched directly or have an active impact on people’s sense of smell or hearing, our sense of a building is formed by our tactile impression. We have very varying responses to timber, natural stone, and metal facades, which are determined either by its sensory qualities or, by association, the smell of the respective material in other contexts (forest, quarry etc.). Some materials are used as a compound element in building systems. The decision as to the choice of a facade material may be based either on the local building tradition and regional availability, or the intention may be to create a deliberate contrast by using a different, foreign material. The texture of the surface (smooth, rough, textured) determines the visual impression of the material, enhanced by the play of light and shadow. Thus the means available to the designer are almost limitless, and their effects can be varied further through the use of detailing, joints and ­colouring. A solid brick facade can achieve an almost textile quality if a suitable brick bond, colour and proportion of openings are chosen.  4 Likewise, a construction that is in contrast to traditional regional methods of building with unworked natural stone may fit smoothly into the overall aesthetic, in spite of the foreign nature of the material.  2 The barely visible jointing of wood shingles suggests an analogy with scales or natural skin. Shingles can be used to cover free forms and also to achieve a flush joint  9 The heavy of the materials between wall and roof. and raw appearance of large-format Corten steel panels makes a building appear closed and forbidding, while the narrowness of titanium zinc panels – resulting from the manufacturing process – and their manual processing ­require a large number of pieces that are nonetheless  5, 7 The changing moods of light simple to arrange from day to night and from summer to winter may lend a building either a sculpturally reflective or transparently  6 layered appearance.

The challenge for the architect lies in finding the right material for the design concept, in converting an idea into specific building materials, colours and surfaces. The necessity of jointing and structuring building components and their effect is enhanced by the play of light and ­colour. It can be perceived as harmonious, agreeable and beautiful, or dissonant and even ugly. Seemingly unbalanced proportion and disharmonies can also be used ­deliberately in order to give a building the desired expression. The scale and massing of a building can also be manipulated. JOINTING There are a number of reasons why joints appear in a ­facade. In the first instance, the potential production formats and the panel sizes of construction materials determine the visible material joints and joint grids. In the case of self-supporting envelopes, for example, the joint pattern is determined by the dimensions of the masonry unit (brick, natural stone) or by the joints between the shuttering boards (cast concrete walls). It makes sense to coordinate the building grid with the grid used for cladding the facade. Deviations from standard dimensions normally lead to increased cost. The expansion and contraction of materials exposed to heat and cold create movement in the facade. This may require additional movement joints, which are either necessary for the loadbearing construction or for absorbing the change in longitudinal dimension of the facade ­material itself. The design of such joints represents a ­difficult detail with regard to weatherproofing. Details have to be designed appropriately for the material and the type of construction concerned so as to ensure that the joints are permanently sealed. The joint is a design element used in architecture and should therefore be considered at an early stage in the design of a facade. The visible appearance of joints can also vary a great deal, depending on the material. For ­example, it is possible to have open joints, recessed (‘shadow’) joints, or joints that are almost flush with the adjoining surface.

1 Texture – principles a Light / heavy b Scale / grain c Elements: homogeneous /  jointed d Light / shadow/ reflection

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MATERIAL AND TEXTURE  27

2 The Maison Roduit, Chamoson 2005, Savioz Fabrizzi: Traditional natural stone and modern fairfaced concrete combined. 3 Housing on Giudecca, Venice, 2002, Cino Zucchi: The homogeneous finish of the render results in a flat texture; the window ­surrounds are coloured to provide ­variation. 4 Conversion and refurbishment of Munich Technical University, 2013, Hild and K: The undulating form of the suspended face brickwork is reminiscent of cloth. 5 Residence, Remerschen, 2014, Valentiny Architects: The use of weathered Corten steel produces a lively patina. 6 Library, Seattle, 2004, OMA: The self-supporting, cassetteshaped steel / glass construction functions as the envelope and ­reflects the surroundings.

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7 The Walt Disney Concert Hall, Los Angeles, 2003, Frank O. Gehry: The order and sculptural effect of the shape are altered by the mate­ rial chosen (metal). 8 Sauna building, Koblach, 2012, Bernardo Bader: The facade is subdivided by the effect of spacing the horizontal battens at different intervals. 9 The ‘Mondholzhaus’, Domat, 2013, Gion A. Caminada: Cladding the curved parts of the building is made simple by the use of small shingles. 10  The Silodam Container, Amster­dam, 2002, MVRDV: Each level has its own colour and identity

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28  Fundamentals

T Y P OLOGY AND USE

There is a close connection between the type of a building and its facade design; this is expressed in how the inner organisation of the building harmonises with the construction and function of the facade and with its overall appearance in urban space. The type of building and its appearance can directly determine the use of a building. Construction components and services installations, as well as local building forms and details, can be expressed in the facade as important design features. The use of a building dictates specific requirements for the building envelope; the spatial distribution of functions and the selected construction grid have a direct influence on the appearance and structure of the facade. Conversely, subdivision of the facade determines the flexibility of use. A practical facade construction grid favours the opportunities for effecting a change of use and thereby has an impact on the cost efficiency and sustainability of the building. Buildings are designed and constructed for different types of use. The way spaces are arranged and used has an impact on the necessary openings in the facade, and hence on the building envelope. It is important to consider aspects of comfort and functionality just as much as the position and size of openings in the facade, which are required for natural light, ventilation and for the ­opportunity to see in or out. With certain building functions, the facade does not ­always express the internal grid pattern on the outside; likewise, the design is not always intended to convey a direct expression. A strict grid inside the building may ­remain visible in the arrangement of windows, or it may be obscured or completely concealed by an additional facade layer. In other cases the facade functions like a filter or mask that envelopes the building and leaves the spectator uncertain of its structure. In contrast, the form of a number of building types results almost inevitably from the use, such as infrastructure buildings or sports venues. Taking the example of a football stadium, it becomes apparent how the building type, form and facade meld into one; the number of seats, the maximum gradient of the grandstands, the roof over the spectators and the open space above the pitch all add up to a readily identifiable sports venue. This inevitable association is rarely so clear cut. In the case of a concert hall, it is possible that the building reproduces the shape of the auditorium on the outside. This is determined by the acoustics, which are affected in turn by the arrangement of the seats and the stage area. Conversely, it is

possible that the auditorium remains concealed behind the envelope, to be experienced only from within. An ­office building readily reveals the parameters – a top priority is the level of light at each workplace. The objective is to allow enough daylight to enter the room so that the cost of artificial lighting can be minimised. At the same time, the daylight must be controllable so that computer work is possible without glare. Direct sunlight – with its associated heat gain and potential glare – is not desirable because it adds to the already substantial internal heat gain from people and electrical equipment, as well as restricting the use of the room. DIN 5035 and the Workplace Directive contain definitions of workplace lighting. Different functions have different requirements for light quality and hence have a direct impact on the design of the building envelope. For example, the all-glass facades frequently used in office buildings go against the technical requirements for light and heat. To enable their proper use, additional measures are employed such as double-skin facades, fixed and movable screening modules, blinds, screens and special glazing. For the user, a  prime issue in the case of more complex systems is that of individual control. Is it possible to override the control of the screening elements manually, or is the solar screening raised or lowered by an electronic control system without the option of intervention? This can create conflicts of interest, because the automatic control system is a reliable device preventing the overheating of rooms. Users’ personal preferences, such as the desire to look out or have brighter surroundings, cannot be ­accommodated. In addition to admitting daylight, the facade is also responsible for thermal comfort in the building. An exterior skin with poor insulating properties results in low surface temperatures at the external walls, which can lead to technical and building physics problems as well as affecting comfort. Pronounced differences between the surface temperature of the facade and that of other room surfaces must be avoided, because the contrast in thermal radiation – as well as the resulting air movement – is perceived as uncomfortable. It is possible to compensate for cool facade surfaces by increasing the indoor air temperature, although this will have a negative effect on the total energy consumption of the building. It follows that the facade is a key interface when it comes to comfort, user-friendliness, building physics and ecology. All these factors – in a telling and recognisable fashion – affect the appearance of building envelopes.

TYPOLOGY AND USE  29

1 Olivetti buildings, Frankfurt am Main, 1972, Egon Eiermann: Ver­ tical and horizontal bars provide a relief to the strict facade grid of the two tower blocks, imparting a slender, floating elegance to the solid volumes. The aesthetic quality reflects the functional requirements. 2 The European Central Bank, Frankfurt am Main, 2015, Coop Himmelb(l)au: The composition of two glass towers rises from a ­polygonal footprint, which is reinforced by the glass envelope of slanting, partially curved, glass ­surfaces. It was not possible to achieve the desired appearance and functionality with commonly available systems; for this reason a new type of facade was developed, called the ‘shield hybrid ­facade’.

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3 Library, Birmingham (UK), 2014, mecanoo architects: The new building for the library comprises three distinct parts stacked one upon the other, transparent and solid rectangular volumes clad with interlocking aluminium rings of different sizes. These symbolise the industrial past of the city and form a decorative ­filter that shelters the interior. 4 The Jacob and Wilhelm Grimm Centre, Berlin, 2009, Max Dudler Architects: The basic motif of the ­library is derived from bookshelves. The strict subdivision of the suspended stone facade expresses the use of the interior. The narrow windows are placed in front of bookshelf areas, while the wide windows provide light to workplaces. 5 Selfridges department store, Birmingham (UK), 2003, Future Systems: The ‘blob’ shape puts the building into context regardless of scale. Fifteen thousand aluminium plates measuring 60 cm in diameter follow the organic, sculptural shape of the building and modify its appearance depending on the angle of light.

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6 Louis Vuitton store, Tokyo, 2014, Aoki Jun and Associates: The perforated front of the building has been designed with reference to the logo of the Louis Vuitton brand and makes reference to the Art Déco past of the Matsuya Ginza city quarter. During the day the external skin appears as a ­homogeneous surface, while at night the LED strips light up the monograms from within the facade. 5

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30  Fundamentals

ENVELOPE AND CONST RU CTION

Every building has an envelope with an inner and an outer face which, depending on the loadbearing structure  SCALE, vol. 3, Support | Materialise, performs a number of protective functions. This may take the form of a solid, monolithic structure or of several different successive  4 ‘filter’ layers, each of which has a specific function. The more recent construction methods offer greater flexibility in the loadbearing structure and hence in the design of the layout on plan. This can affect the positions of the walls and of the envelope. The separation of the loadbearing structure and the envelope goes hand in hand with the dissolution of the facade into distinct layers. Each ‘filter’ layer performs its own function, each building component is potentially a design element in its own right, including the columns and other loadbearing elements which are separate from the envelope. If the envelope and the loadbearing structure are one and the same, this is normally referred to as solid construction; a construction in which the envelope as the outer facade element is separated from columns and floor slabs is ­referred to as skeleton or frame construction. As a means of bracing, in large buildings the floor slabs are often connected with the solid building core; the thermal envelope remains nevertheless independent of the loadbearing structure. The clear expression of structure is compromised when overlaid by the secondary construction and industrially produced elements. This type of construction method is referred to as hybrid, as it employs a variety of construction systems. Therefore the choice of construction and materials involves aesthetic, economic and ecological

considerations which are directly connected with the function of the building component. The move away from solid building components with a large mass towards high-performance filigree elements increasingly leads to greater freedom with respect to construction and conceptual design. It means that solutions can be tailored closely to each brief. Independently of whether the focus is on the recognisability of the structural elements of the construction or on conceptual aesthetics as the primary design objective, the building construction must fulfil the following requirements: – Functionality, compliance with the principles, rules and regulations of construction; – Freedom from defects in execution and cooperation amongst the trades, including operation and maintenance; – High-quality design and appearance, from the installation through to the graceful aging of the facade; – Sustainability in terms of the responsible use of resources and the energy needed for the production, use and disposal of the construction material. As the requirements for the construction of building ­envelopes become more complex, more expert know­ ledge and experience is needed. It is not just building physics that makes high demands of the facade: all aspects of building design are involved. For this reason, good coordination and communication among the members of a qualified design team is the key requisite for the fault-free execution and function of a high-quality building envelope.

1 Apartment block in Hamburg, 1920s: The solid external wall with individual windows is typical of the Expressionist brick architecture of the 1920s. 2 Office building, Hamburg, 2011, Henning Larsen Architects: The glass facade consists of an inner envelope of timber window elements and an external mullion /  transom facade with single-glazing, which makes natural ventilation possible. The solid sections are part of the solar screening system.

1

2

3

3 Holiday home, Salt Point, 2007, Thomas Phifer: The holiday home is shrouded in a screen of perforated stainless steel. Depending on the changes in light, the facade changes from opaque to a transparent envelope and blurs the boundaries between interior and exterior.

ENVELOPE AND CONSTRUCTION  31

4 Requirements of a facade Interface between inside and ­outside Interplay between functional requirements and design aspects.

SAFETY AND PROTECTION Fire protection Fall protection

LIGHT / COMFORT Daylight incidence Views to the outside Boundary between private and public Glare protection, light control

SERVICES INSTALLATIONS Controls – individual, central Flexibility of use Activation of building components for the purpose of storing energy, heating and cooling

THERMAL COMFORT Room climate / temperature Constancy of temperature Heating and cooling Airtightness Protection against cooling down in ­winter Ventilation of rooms, exchange of air

ACOUSTIC COMFORT Sound insulation

InSIDE

DESIGN Topography Context Climate Type of building Expression, symbolism Composition, proportion Material, texture

SUPPORT FORM

INSULATE PROTECT

Function

CONSTRUCTION AND I­ NSTALLATION Primary structure, loadbearing structure Secondary structure Local resources Prefabrication, installation on site Construction sequence, logistics

OUTSIDE

4

THERMAL REQUIREMENTS Climate envelope Thermal and solar protection Glare protection Wind barrier Protection against rain and humidity

SECURITY AND PROTECTION Fire protection Fall protection Radiation, noxious substances Intrusion, vandalism Sound insulation

ACOUSTIC REQUIREMENTS Sound absorption

SERVICES INSTALLATIONS Photovoltaics, collectors Geothermal probes, heat recovery Solar thermal collectors

32  Fundamentals

SOLID CONSTRUCTION In the case of the single-skin solid wall – which performs the functions of structural support, insulation and protection in one layer – a distinction is made between ‘warm’ and ‘cold’ facades.  1 In the ‘warm’ facade, the thermal insulation layer is fitted directly on the loadbearing layer. When this insulation is on the outside, the outer surface must also provide protection against the weather in order to avert damage to the construction. When the insulation material is placed on the inside face of the construction, it is possible to achieve an improved energy standard without changing the exterior appearance (for example in the case of refurbishment or in historic buildings). Internal insulation must be carefully designed and its installation must be closely supervised. An important aspect of the design is the simulation of the flow of moisture over several years. Nowadays, mineral-based internal insulation systems are available with physical properties equivalent to those of external insulation. A ‘cold’ facade consists of several layers which perform different functions in terms of construction and building physics. The inner skin (consisting of the loadbearing structure, the thermal insulation and the sealing layer) is separated from the outer skin (weather protection layer) by a ventilated cavity. The separation of the insulation layer from the layer facing the weather protects the critical parts of the construction, such as the base of the wall and the roof parapet, as well as areas where the insulation and sealing are offset next to openings. Exterior cladding can consist of a wide range of materials, resulting in different loads and providing different design options. In this type of construction, it is important to ­ensure that the points at which the exterior cladding is fastened to the loadbearing structure are detailed and installed in a way that does not permit

any vulnerability where they penetrate the insulation layer. A solid construction is often chosen for an exterior wall as the result of a conventional attitude. Putting up buildings with brick walls and concrete floors is often deemed to be the natural solution. In most cases, this method is the most economical because the people involved in the execution do not need to have specialist knowledge. Other criteria may be longevity and retention of value. The limitation of such a construction lies in its heavy weight. This means that in buildings over 25 m high, the economic advantages dwindle while the site logistics and transport of material during the construction phase become more expensive. The greater component thickness of highly insulated masonry units results in an unfavourable proportion of footprint area to net floor area. Solid structures can store heat over longer periods, and give it off again slowly. In solid construction, orthogonal designs are common, although it is also possible to build walls in slanting, amorphous or kinked shapes using brickwork or concrete. Solid construction necessitates either adding elements (bricks or masonry units) or casting monolithic structures (concrete). The solid structure of the wall means that the material can be visible both externally and internally, which can provide a special experience in terms of touch and the appearance of the jointing. The weathering quality of a single-skin system can be improved by applying an additional layer such as rendering, or back-ventilated external cladding in front of insulation. Solid construction may also take the form of a solid wall with an outer layer of facing bricks, or a cavity wall (common in Anglo-Saxon countries), which involves a ­ventilated cavity between the outer and inner leaves. However, the effect of suspended cladding that consists 1 Wall construction types a Single-skin b Double-skin, external insulation c Double-skin, internal insulation d Multi-skin, ventilation in front of the insulation plane

1a

b

c

d

ENVELOPE AND CONSTRUCTION  33

Solid construction

Single-skin

Skeleton construction

Masonry construction / face brickwork  p. 50

Fair-faced concrete Log construction, visible  p. 58

Aerated concrete blockwork, rendered Highly thermally insulating masonry, rendered

Aerated concrete blockwork, with cladding Highly thermally insulating masonry, with cladding

Traditional timber frame ­construction, timber skeleton construction, with insulation and cladding Timber frame construction, with insulation and cladding  p. 78

External insulation layer: Insulated concrete construction with suspended cladding of prefabricated concrete panels

External insulation layer: Steel skeleton construction with curtain wall facade

Internal insulation layer: Fair-faced concrete construction with ­insulation, protective inside lining

Composite thermal insulation ­system, with cladding

Log construction with insulation, protective inside lining

Internal insulation layer: Timber frame construction with internal insulation

 p. 80

 p. 100

Concrete skeleton construction with internal insulation  p. 134

External insulation layer: Masonry construction, single-skin, with insulation, rendered or clad Insulation within the construction: Sandwich systems, with several ­layers, insulated, face layer

Concrete construction, single-skin, with insulation, rendered or clad

 p. 80

Timber panel construction, with insulation and cladding Suspended back-ventilated ­facades, single-skin, insulated, air gap, ­envelope with exposed material

Insulation within the construction: Masonry construction, double-skin, with insulation, face brick or rendered  p. 84

Fair-faced concrete construction, double-skin, with insulation,  p. 54

 p. 90

Multi-skin

Integrated insulation layer: Membrane, integrated air gap  p. 98

34  Fundamentals

of ‘solid’ materials is different to that of a wall built monolithically. This is due to differences in the type of jointing, the junctions between building components and the visible movement joints. In traditional masonry construction, the width of windows and doors was limited because the width of arches built with masonry units over these openings was limited. Such facades usually have a balanced proportion of solid wall to opening. With the introduction of reinforced concrete elements for use as lintels over openings and in loadbearing walls, it became possible to design larger openings in solid construction too, which has led to a new aesthetic.

from the edge of the building, while the secondary structure – in this case the facade and exterior enclosure – can be placed outside the building’s structure. This means that, for the first time, the size of window openings is no longer limited and fenestration can be arranged in bands, as part of a grid facade, or even as full glazing mounted from the bottom up or suspended from the top.  4

The diversity of form in contemporary architecture primarily depends on the continuing development of this construction method. The skeleton construction method does not provide storage mass in the form of walls, so this function must be performed by additional layers. The complexity of the system makes it necessary to think in  terms of strict hierarchies and orders, and requires ­disciplined detailing, in order to be able to achieve ­cost-­efficient production and installation.  5 Advanced ­construction methods use multi-layered assemblies. Different materials and construction elements, each with special characteristics, are installed such that they can fulfil the complex requirements made of the building ­envelope as a unit. Facade cladding systems with backventilation, in which the visible facade material is separate from the insulated wall construction, have become popular. The materials used, as a consequence of their specific properties, determine the appearance of a facade, as well as its construction system and its building physics functionality. The selection of materials and the dimensioning of elements are limited by their respective properties and by the limitations associated with production and installation, be it industrial or craft-based. The external skin can be installed as back-ventilated rainscreen cladding in front of the insulated construction; typical examples are metal sheeting, fibre cement panels, wood-based panels, timber cladding and plastic p ­ anels.

SKELETON CONSTRUCTION With the disappearance of the solid wall owing to the use  of new building materials such as steel, cast-iron and glass, for example in the imposing greenhouses by ­Joseph Paxton in the late nineteenth century, the principle of skeleton construction – already known from timber frame buildings – emerged as an alternative that promised the efficient use of material. The loadbearing function of the structure is performed by individual elements such as columns, foundations, floor slabs and plinths, thereby reducing the vertical forces and hence the quantity of material required. The separation of the building structure into loadbearing and non-loadbearing elements results in a loadbearing skeleton, which provides the designer with greater freedom in terms of ­layout and facade design. In this kind of construction, the thermal envelope is also the element that encloses space. While the facade elements were initially placed between columns and slabs, this technique was superseded by the construction known as a ‘curtain wall’, in which the facade elements are fitted full-height in front of the structure. The primary structure is moved inwards

1 Functions of facade layers from inside to outside: Vapour seal Support Insulation Weather-protection layer

2 Typical functions of a solid ­external wall, which may be ­performed by just one material: a Rain protection b Mechanical protection c Thermal insulation d Structural integrity e Sound insulation f Fire protection g Thermal storage h Airtightness / vapour-tightness i Protection against humidity /  wind

h, b d, e, f, g c c, e i a, b a, b

2

1

3

d

3 Typical functions of a ­transparent glass facade: a Solar screening b Light control c Glare protection d UV-protection e Black-out

ENVELOPE AND CONSTRUCTION  35

Cladding panels or a suspended facade may also consist  of materials such as brickwork, natural stone and ­concrete, which historically are more associated with the solid construction method. This makes efficient use of  the material and its positive mechanical properties.  1, 2

Every design decision concerning the composition and proportion of such a facade is governed by the principle of the grid. This grid may have the same dimensions as the grid of the primary structure, or it may be offset with different field widths, or it may be completely independent of the main grid, forming the fit-out grid for fitting out the interior. Repeating the module dimensions helps to reduce the cost of site logistics and of manufacturing prefabricated units.

4 a

4 Transfer of loads

b

c

Horizontal: Negative wind pressure Snow loads Strain forces resulting from ­temperature fluctuations, material expansion etc. Vertical: Own loads Strain forces resulting from ­temperature fluctuations, material expansion etc. a Suspended b Standing c Standing over two storeys

5 Position of the thermal envelope and the associated design options in skeleton construction a In front of the primary structure b Within it c Behind it

5a

b

Position

Secondary structure

Position

in front of the primary structure Advantage

Design freedom for the interior Transparent corners No thermal bridges

Facade externally flush

Position

Primary structure

in the plane of the primary structure

in front of the secondary structure

Advantage

No connection surfaces on the inside

Advantage

No columns on the inside

Disadvantage

Closed facade corner

Disadvantage

Restricts view to the outside

Detailing of the thermal insulation of the

It is necessary to decouple the floor slab

face of the floor slab and of the primary

thermally in the facade plane

Additional fire protection required between

structure

Connections create thermal bridges

the facade and the structural shell

Connections create thermal bridges

Higher cost

Prevents fire flashover in the facade plane Disadvantage

c

36  Fundamentals

PROT ECTION

Building envelopes protect people from the effects of the environment and therefore any facade construction should have a long service life.In particular this refers to the technical and building physics requirements – from the outside and from the inside – which must be fulfilled by the material and construction. For example, a simple steel sheet is capable of withstanding water and vapour pressure, but is inadequate in terms of thermal insulation. Conversely, thermal insulation layer which is not sufficiently protected against moisture ingress will become saturated with water and gradually lose its effect. However, when these two materials are combined in the form of a sandwich element, they represent a fully functional facade envelope. There are some materials that fulfil all functions with a thickness of only few centimetres (for example, insulating glazing), while other constructions need many layers in order to achieve the same result. The two main requirements for a building envelope are, firstly, protection against damp and precipitation and, secondly, thermal protection against cold in winter and heat in summer. Respectively, thermal protection has the aim of reducing energy losses from the interior, or of preventing heat gain. This means that the envelope has an effect on the energy requirement for heating in winter and on the internal temperature or the energy demand for cooling in summer. The thermal transmittance or heat transfer coefficient (U-value, W/m2K) of a construction defines the amount of heat that flows through a building component under defined boundary conditions (heat transfer) and is used to calculate the key energy values of a building. The smaller the thermal transmittance of a building element is, the better are its insulating properties, making it easier to save energy and reduce costs. In  addition, the surface temperature of the facade on the  building’s interior affects the perceived comfort of the user. The potential for better U-values lies not only in the improved physical properties of the insulation material, but also in improving the construction of facade frames and openings, as well as the glazing – using thermally insulated frames, surface coating on insulating glazing and new compound materials in the non-transparent areas. Energy is not only lost through transmission, but also through leaks and joints in the construction. These leaks can be the cause of considerable structural or material problems. Joints or cracks provide a path for moisture from the internal air to migrate into the building fabric, where in winter it may precipitate as condensate and make the fabric damp, which can potentially lead to the destruction of the components and the loadbearing structure. Furthermore, the accumulation of water in insulating layers results in a significant worsening of the insulation properties.

Considered from the outside, joints in a building envelope enable rainwater to enter directly or via capillary action, which can also lead to building defects. Joint permeability also has a direct effect on the transmission of airborne noise. The design of the detailed construction is therefore critical in order to ensure the necessary airtightness (from the inside) and wind-tightness (from the outside), and careful supervision on site is required. Airtightness can be achieved by installing special membranes, for ­example, whereas in solid construction a continuous layer of plaster or render is sufficient. External protection against precipitation is just as important as providing adequate thermal insulation. Many defects in buildings result from badly matched or faulty detailing of the facade construction. Even seemingly tried-and-tested constructions, such as framebased facades, and the respective connections with the building fabric have many potential failure points, and care must be taken in their design and on-site assembly. In wall construction, at least three layers are required to meet contemporary requirements: those for loadbearing, insulation and weather protection. In a normal masonry wall, the brick or block itself fulfils the insulating, loadbearing and sound insulation requirements. The inner plaster finish ensures the airtightness of the construction and provides the visible enclosure. The exterior layer of render protects the structure against precipitation. In such wall constructions, today’s requirements for thermal insulation can be met by using masonry units with cavities filled with an insulating material or by aerated concrete blocks. Conventional masonry units can also be used if the structure is combined with an additional external layer of in­ sulation (thermal sandwich insulation system). However, without additional measures this type of construction is less resistant to mechanical impact from the outside. Likewise, the appearance of render applied to such a sandwich system is different from that applied directly to masonry – the insulation layer will be perceived both visually and acoustically (when tapped upon). This example shows that the designer needs to weigh up the advantages of the various factors such as perception, durability, production costs, sustainability and disposal and recycling aspects. Classic defect areas – in addition to the base and the parapet / roof connection – are the joints between the building components and the points at which fastenings and services penetrate the insulation layer. Offsets in the plane of insulation and sealing materials must also be given special attention, as should the detailing of vertical and horizontal external and internal corners with respect to thermal bridging. Furthermore, the interior fit-out elements, e.g. partition wall systems, are usually in contact with the thermal envelope – something that needs to be taken into consideration in the facade design.

Diagrams of facade functions Effects and measures 1 Solar irradiation a Heat b Light 2 Precipitation, snow load a Rain b Snow c Ground moisture 3 a b c

Relative humidity, water vapour Single-layer Multi-skin Multi-layer

4 Risk of cold bridges where ­insulation or separation of materialsis insufficient a Plinth b Balcony c Flat roof

PROTECTION  37

2a

1a

1b

2b

2a

IMPACT FROM THE ­EXTERIOR

NECESSARY CONSTRUCTION MEASURES, such as

Solar irradiation, light

Solar screening, glare protection, light control, black-out, UV-protection (paint, material)

Solar irradiation, heat

Insulation, use of passive solar gain, reflection, surface colour

External air temperature, ­summer

Insulation, storage mass

External air temperature, ­winter

Insulation of building components, storage mass, reduction of thermal bridges, ­airtightness of construction

Precipitation, vapour

Protection against the ingress of water or driving rain, rain seal, leak-proof roof membrane, protection via construction elements e.g. canopy, roof overhang, plinth, fall in the terrain, drainage

Building loads, ground motion

Foundations, structural calculations, special construction methods (e.g. earthquake stability)

Snow load

Sealing measures, structural measures

Wind load

Air sealing measures, structural measures

2c

1, 2

Odour

Air seals, filtering

Noxious substances in the air

Air seals, filtering

Fire

Active and passive fire protection ­ easures (building material class, m fire resistance)

Noise

Sound insulation measures

Views in

Screening measures

Mechanical impact

Choice of material for external ­ ladding, c protection via construction elements

Soiling

Choice of material of external cladding, protection via construction elements, cleansing aids

IMPACT FROM THE ­INTERIOR

NECESSARY CONSTRUCTION MEASURES, such as

Air temperature winter (interior)

Insulation, expansion joint, avoiding cold bridges

Relative humidity, vapour pressure

Vapour seal, discharge of humidity, discharge of condensate, back-ventilation

Fire

Active and passive fire protection ­ easures m (building material class, fire resistance)

Noise

Sound insulation measures

Mechanical impact

Choice of interior cladding material, protection via construction elements

Soiling

Choice of interior cladding material, protection via construction elements

a

c

b

3

c

b

4 a

38  Fundamentals

ECONOM Y AND PROCESS QUALIT Y

processes

and technical

they can be imple-

raw materials,

in favour of subse-

­different stakeholder

and construction

­possibilities; socio-

mented in the

recyclability of con-

quent increase in

groups;

­process

cultural ­influences,

­construction;

struction materials,

density and revitali­

creating local identity

sustainability and

integration of these

access to alternative

sation;

for individuals and

ecology require-

measures into the

energy supply

flexibility of use

­society;

ments;

­design

­concepts, change-­of-

use models (mixed

producing and

use investment and

use);

­assessing workable

location factors;

infrastructure and

solutions as basis

sparing use of con-

mobility concepts

of a decision;

struction land / sealed

link between all those

surfaces

and production ­process Design, production process, life cycle

i

i o - c u lt u ra l

oc va l

mo

Re

Quality



integration of the

­monitoring the ­design

Cost



Participation models;

value-creation model

Deadline



Modification of the

mentally compatible

lo gy

Availability of environ-

possibilities and how

Eco

Analysis of technical

user requirements

S

Analysis of location,

requirements and

n

n

Drawing up the user

supporting and

tio

sio

Society

Drawing up the brief;

involved in the design

Process / time factor

Property industry

c on stru c

ver

Construction industry

N ew

Con

Specialist engineer

The building



Architect

Design, functionality, technology, cost-efficiency, operation, time, socio-cultural influences, economy, ecology

Ec



Tasks

User, operator

n ce s

y

Client

Requirement

l ue nf

om

Position

these teams will take different options into consideration and thus allow for the complexity of the tasks, evaluating different solutions in accordance with requirements and priorities. Any solution found for an individual building may not necessarily be transferable to other projects, but it can contribute to a basis and inspiration for a ­holistic approach to facade design. When designing facades, the strong interdependence of the parameters of cost, quality and deadlines make it necessary to consider and evaluate different construction methods, details and materials and to find a suitable solution in agreement between the client and design team. The first step in creating the evaluation matrix – construction, material, details, cost – for design options is to define the requirements for the facade, which are normally supplied by the client or possibly the user. The objectives must be defined at an early stage and the client / user has to contribute to many decisions during the ­design process. For example, any subsequent change in the energy-related quality of the building envelope has a severe impact on the services installations concept. These parameters can be influenced most effectively at an early stage in the design and development process. It is important that conceptual design quality and functionality are in harmony – within the set budget. Unrealistic cost estimates and ill-considered economies always have a negative impact on quality and the subsequent costs during the use phase. For example, a rendered facade on a tower block may reduce the initial cost of investment compared to a high-quality metal facade, but the sub­ sequent cost involved in the maintenance/renewal of the facade at shorter intervals can very soon wipe out this advantage.

on

The increasing demands made of buildings are not only apparent in the construction details, but also in the design and construction process. For some time now, the architect coordinating a large project has had additional support from specialist facade designers, air-conditioning specialist, building physics specialists and energy ­experts; nevertheless, basic competence in these specialist areas is still required for the purpose of their ­coordination. The architect operates as a coordinator and communicator and, equipped with adequate technical know-how, ensures that construction projects meet economic and commercial criteria. In addition to the classic areas of architectural expertise, a holistic design approach also requires knowledge of the ecological and economic aspects of design, production, installation, maintenance and servicing. Extensive knowledge of new developments, technologies and available materials is also required. Strategies and assessment criteria for the correct selection of a facade solution are required at an early stage in the design in order to avoid subsequent changes which result in high costs. Similarly, it is important to be aware of changing standards and guidelines and to take into account any new technologies and system modifications. It follows that a competent design team is required to control the design process, which will make far-reaching decisions either in agreement with the building client/user or, sometimes, on its own. The level of process quality is evident in the cost planning, the control of deadlines and the quality of the building design. However, the real conceptual design process is not covered by these criteria and evaluation systems. Most intelligent facade concepts require the networking of interdisciplinary teams for their creation;

1 Relationship between integrated design, sustainability and process quality

2 Relationships of tasks and ­participants in the building process, and effects on design, construction process and life cycle

ECONOMY AND PROCESS QUALITY  39

POTENTIAL FOR OPTIMISATION An important component of the optimisation of process quality is an exact definition of the task. What are the requirements that the facade of an office building has to fulfil? How transparent or opaque is the building to its surroundings? What additional loads can be absorbed by an existing building when the facade is upgraded for the purpose of energy optimisation? Should the building ­envelope have a flat appearance, with the openings being flush with the facade, or should the facade be structured by the grid of a construction system? What is the orientation of the building and how does this affect the use of daylight and the outlay for energy and maintenance? For example, although a south-facing facade ­requires solar screening and glare protection, it may, ­owing to passive solar gain in winter, nevertheless be an economic option, provided rigid – and hence low-maintenance – screening systems can be fitted. Appropriate ­solutions may be found more easily by questioning the functional requirements with an open mind and analysing the local parameters. The selection of materials used and their processing has an influence on construction time and cost. Constructions made of materials that are simple to install – such as back-ventilated timber cladding – can be produced economically. By contrast, a back-ventilated natural stone facade is significantly more costly; the reasons are both the cost of the material itself and the fastening technology which, owing to the great weight of the stone, must consist of durable, corrosion-free material. Generally speaking, large and heavy components can only be installed with the aid of appropriate machinery (such as a

Phase

Selection of location

Start of design phase

Start of construction

Construction period

Use period

Change of use /  demolition

Processes

User requirements

Integrated design with all

Selection of sys-

Selection of contractors

Maintenance, servicing,

those involved

tems / material, produc-

through to handover

cleaning

Recycling or disposal

tion, modes of transport through to assembly on site / prefabrication Degree of

High degree of influence / 

Medium degree of influ-

Low degree of influ-

Low degree of influence / 

Large cost factor

Large cost factor

influence / costs

low cost

ence / 

ence / high cost

maximum cost

depending on solution

depending on solution

medium cost

Degree of influence on cost

Cost

3 Effect of processes, costs and design freedom on building phases. Analogous to the German BNB system (BNB = assessment system for sustainable construction), see also Jones Lang LaSalle (2008)

crane) and require an installation team with special knowhow. Special solutions and non-standard formats almost always result in increased costs for both production and transport, and an associated extension of the construction period, unless they are produced in large numbers. In addition, the designer can influence the cost, quality and time frame of the construction by selecting a production method (prefabrication, part prefabrication or installation on site), that is suitable for the size of the project. A high degree of prefabrication will normally reduce the time required for construction on site, but extend the time required during the design phase. In contrast, assembling components on site can lead to a longer construction period, but may be more economical because local tradesmen who need shorter lead times may be available. As a rule, the use of standardised components, shorter transport distances, repeats of the same design details and simple loadbearing structures, as well as an appropriate choice of material, all result in a lower construction cost. Commissioning the completed project is likewise part of  quality assurance; in this context it is important to ­remember that the efficiency of a system can only be ­assessed after completed heating and cooling seasons. The subsequent tuning of building services becomes an important component of building maintenance. The quality of the installation is a vital element in ensuring the fitness for purpose and the durability of a facade. Due to the conditions on building sites and the primarily manual construction process, the execution of the interface between envelope and loadbearing structure requires great precision and attention to detail in order to avoid future defects resulting from thermal bridges or leakage.

Lifecycle-optimised design

80 to 85 % of total cost 15 to 20 % of total cost Conventional design

Time

40  Fundamentals

ECOLO GY AND LIFE CYCL E

The construction industry can potentially make a big contribution to sustainable building in the sense of the careful use of land and material resources, the conservation of energy and reduction of emissions. The construction industry – including building construction, civil engineering and infrastructure – accounts for 50 % of raw material consumption worldwide. In Germany, 60 % of waste is produced by the construction industry; furthermore, in Central Europe, approx. 50 % of energy generated is used for the operation of our buildings. In view of the fact that our planet’s energy and material resources are finite, it is important to select materials according to ecological criteria – from the extraction of the materials to the construction and maintenance of the building as well as its demolition, disposal and recycling. The awareness of and sensitivity to environmental issues is increasing in our society; this should be matched by ­appropriate qualities in the design, use and efficient maintenance of buildings. In order to ensure this while maintaining typological and conceptual diversity in building construction, scientists have developed assessment systems and indicators for the sustainability of buildings over the last decades, which make it possible to assess and classify buildings according to standardised criteria. The bestknown certificates – which can be summarised internationally under the term ‘green building’ – are BREEAM and LEED, developed in Great Britain and the U.S.A respectively. Assessment methods have also been developed for use in German-speaking and European countries, such as the DGNB (German quality seal for sustainable building) in Germany and the Minergie standard in Switzerland. The key indicators of sustainability can be found in all ­assessment systems: ecology (building materials, water, type of site / land use, energy / technology), economy (planning processes / management, innovation and ­design

processes, transport) and social benefits (functionality, health and wellbeing, conceptual design quality). These issues not only relate to buildings overall, but also concern the definition of the requirements for building envelopes. Apart from the energy consumption of a building, which ecological factors must be taken into account in the design of a facade? What is the influence of the service life of construction materials and assemblies on their treatment and maintenance?

o

c

 / d i

 R e

io n

ru

g /

c lin

olit

Up cy

Profitability ← Construction costs ← Maintenance costs ← Location and surroundings







d ove r / o c c u p a

← Functionality ← Design quality

te

io ns



n

n

t io

x  / e

← Demographic change

Dem

Commercial factors influencing the service life

Ha n

Mo

d ern

isa tion



C

on ve rs i

on

2

st

n

n»

Impact / wear by users → by weather →

on

tio

io

Maintenance service intervals → Proper workmanship →

g li n

»C

ru c

ct

Quality of building materials → Finish of construction ­elements →

yc

Design

n st



sp

l sa

55 %

Facade

25 %

Fitting-out

20 %

Services installations

20 %

1 Content of primary energy in the various parts of the building

PRIMARY ENERGY An important aspect is the primary energy content (PEC) of the materials used, which describes the energy embodied in a material in its production, transport, storage, ­installation and disposal – also referred to as ‘grey’ or ‘embodied energy’ It follows that materials with high primary energy content are those whose production consumes a lot of energy, such as metal, glass or plastic. Materials with low primary energy content include clay, gypsum and renewable raw materials such as timber. However, materials with low embodied energy from the production process may still have a significantly increased PEC as a result of their processing or transport requirements. When comparing facades of different materials, it becomes ­evident that the amount of embodied primary energy can  vary significantly, e.g. a brick facade has approx. 400 KWh / m2 PEC whereas a timber facade has only approx. 80 KWh / m2 PEC. To put these figures into a different context: the energy embodied in the bricks used to build a single-family house is roughly equivalent to the ­energy used in that building over a 15-year period under normal conditions. However, the higher amount of energy in a brick facade compares less unfavourably with that of a timber facade when taking into account its longer service life, which may be two to three times as long. N ew c o

Technical factors influencing the service life

1

Structural shell

← General circumstances /  income levels

2 Commercial and technical ­factors influencing the life-cycle of a building.

LIFE-CYCLE COST / ECO-BALANCE Frequently the cost of a building is assessed on the basis of construction costs only, although clearly there are additional costs that arise after completion of the building for maintenance, servicing and upkeep. Over the long term, these exceed the production costs. Currently, calculations for the cost efficiency of projected buildings work on the basis that, of the total cost, 20 to 25  % are investment costs and 75 to 80 % are costs resulting from the operation of the building. When the whole life cycle of a building is taken into ­account, the scope is broadened to include not only the construction cost and the operating, maintenance and value-preservation costs, but also the costs of demolition and disposal.  2 The notions of life-cycle cost (LCC) and eco-balance (LCA – life-cycle assessment) were originally developed for industrially manufactured products. When transferred to the construction industry, they were differentiated into two frames of reference. The first concerns the technical service life of the essential building components: How long does a building last? The second concerns the usa­ bility of the building: What duration of commercial use can be expected? The term ‘technical service life’ refers to the period over which the building, including its instal 4 lations, is available before it is demolished. The duration of the commercial use of a building is subject both to its fitness for a given purpose and to the economics of real estate investment. Factors such as the pay-back of construction costs, patterns of demand, the development of the location, and functional and aesthetic design qualities can have a significant impact on the commercial viability of a building during its service life and can even lead to its premature demolition. The holistic

Socio-cultural and functional quality

Economic quality

Ecological quality

ECOLOGY AND LIFE CYCLE  41

Technical quality Process quality Location characteristics

3

3 Selection of certificates /  assessment categories LEED (USA): Careful use of resources (land / mineral resources), water efficiency Energy and atmosphere Materials and resources Interior space quality Innovation and design process BREEAM (Great Britain): Management Energy, water Land resource consumption and ecology Health and well-being Transport, material Pollution DGNB (German quality seal for ­sustainable building): Ecology, economy Social and functional aspects Technology, processes, location BNB (assessment system for ­sustainable building), contains ­assessment criteria for the ­construction of German government buildings: Ecology, economy Social and functional aspects Technology, processes, location

Building component / layer 4 Technical service life of building components (according to manufacturers’ information)  Appendix,

External wall, loadbearing – concrete exposed to weather

p. 156

5 Cleaning intervals for different facade materials (according to manufacturers’ information)

4

assessment of life cycles makes clear the direct inter­ dependence of ecology and economy. The shorter the service life of a product and the more frequently a component has to be replaced during the commercial lifetime of a building, the higher the ­energy consumption (PEC) and the greater the burden on the environment; the costs of removing, disposing of and replacing components rise, and this too affects the eco-balance. Maintenance The choice of building materials is also affected by the required frequency of servicing and maintenance, because the subsequent costs of these far exceed the construction cost of the building components. On the other hand, proper maintenance of the facade contributes to its longevity. Facade glazing, windows and exterior doors require quarterly cleaning, whereas coated metal facades have an average cleaning cycle of two to three years. By comparison, natural stone and untreated solid timber are very long-lived.  5 Accessibility is crucial to cleaning and maintaining facades. Good detailing can protect facade elements and thus prolong their service life. Higher buildings with large glazed areas require either shading ledges / gratings that can be walked on for maintenance, or lift platforms / cages. Additional hydrophobic coatings, as well as roof projections, can significantly extend cleaning intervals e.g. for glass. When assessing anticipated soiling, local conditions must be taken into account; for example, the expected cleaning intervals in an industrial area with high emissions, or near busy roads, are significantly shorter than those in a quiet, residential suburb.

av. service life, years 70

Facade material

Cleaning cycle / years

External wall, loadbearing – brick, calcium silicate brick

120

Aluminium cladding

2

External wall, non-loadbearing – softwood, e ­ xposed to weather

45

Zinc sheet cladding

3

Enamelled steel sheet cladding

1

External wall, non-loadbearing – hardwood, e ­ xposed to weather

70

Exterior paint coating – impregnation on wood

15

Natural stone

20

Exterior render – cement-based, lime-cement-based

40

Prefabricated concrete elements

12 20

Glass

0.25

External render – thermal insulation sandwich s ­ ystem

30

Clinker brick

Cladding on substructure – natural stone

80

Solid wood, fully coated

Cladding on substructure – aluminium

45

Solid wood, untreated

20

Substructure – stainless steel

45

Fibre-cement tiles, coated, small format

10

Substructure – timber

30

Fibre-cement board, coated, large format

2

5

5

42  Fundamentals

REF URBISHMEN T, WAST E AND RECYCLING

REFURBISHMENT In addition to the new construction of buildings involving the design of building envelopes that meet contemporary technical requirements, a large proportion of the construction volume to be expected in Europe will involve the refurbishment and renovation of existing buildings. There are many ways of dealing with existing buildings, ranging from simple reinstatement in which only the necessary repairs are carried out, through to energy upgrades and structural conversion work with the aim of improving the quality of the building by increasing its functional flexibility. A holistic assessment using the lifecycle model as a tool can be useful for determining a ­decision in this respect.  p. 40, Ecology and Life Cycle The refurbishment and renovation of buildings can be ­economically and ecologically interesting alternatives to demolition and new construction. This is not only a question of better energy efficiency through upgrades and new installations to improve sustainability, but also one of structural measures. An advantage here is the fact that the building can be retained, for example in inner city locations where new buildings would require new approvals, which may be subject to conditions relating to density, height and the distance from other buildings. The infrastructure, identity and services of city quarters can thus be retained while carefully developing the building stock to accommodate new functions and uses. Retaining the substance of buildings reduces the cost of construction; for example, if the facade of an existing office building has elementary defects because of an unfavourable grid dimension and the restricted ingress of daylight, this can be remedied by ­replacing the facade. The adaptation to a more economical facade grid improves efficiency and functional flexibility and thus makes the building more attractive to prospective tenants.

1

In addition it is possible that, beyond the purely technical functionality, the image of the building is improved. For example, the conversion of a residential post-war tower block in Paris demonstrates intelligent intervention involving changes to the basic structure.  1 By contrast, the adaptation of the facade of a residential tower block, owned by the Munich students’ union, to contemporary requirements with respect to energy standards and fire safety demonstrates how refurbishment is possible without losing the expressive character of a  2 building. Requirements specific to the function of a building also play a role, for example it may be necessary to change the structure of a building in order to adapt it to a new function. Typical examples are defunct industrial and ­office buildings which are converted to residential or cultural use, or the use of historic buildings as hotels and restaurants. These conversions, fit-outs and extensions can be made distinct from the original fabric and thereby use the facade to confidently demonstrate the changes that have taken place. Alternatively, they can enter into a restrained dialogue with the existing style or take it further in much the same spirit. Where a historic facade consists of natural stone, bricks or timber framing, it is important to ensure that the original character of the building is not lost. Likewise, mouldings, window and door reveals and other valuable historic embellishments may be of a quality that warrants preservation. Proper professional refurbishment requires knowledge of historic materials and traditional building methods. The decision in favour of one or the other design approach is arrived at through consideration of the respective design task, the user, the importance of the building itself, the built surroundings and – last but not least – with the agreement of the authorities and listed building department.

1 The Bois le Prêtre tower, Paris, 2011, Frédéric Druot with Lacaton & Vassal: A 17-storey apartment block – built by Raymond Lopez in 1958–61 – was extended by a prefabricated module suspended in front of the facade for the purpose of zoning and increasing the available living space. In addition, movable solar screening panels were fitted to conserve and store energy in the modules.

REFURBISHMENT, WASTE AND RECYCLING  43

Refurbishment 2 Student housing in the Olympic Village in Munich, refurbishment 2012, Knerer Lang: A new curtain facade was developed as part of the overall refurbishment. A lightweight concrete frame system has been placed in front of the existing, newly insulated facade. The previous GRP panels underneath the windows have been replaced by 2a ­solid panels with aluminium cladding, in combination with a new ­window element. a Prior to refurbishment b Following refurbishment 3 Office building on the Neue ­Balan campus, 2012, Oliv Architects: The energy upgrade of the existing facade was used to increase the grid dimension of the ­facade in order to improve the ­efficiency of the layout and thus to create more attractive lease properties in the new campus. a Prior to refurbishment b Following refurbishment

b

3a

b

New building with recycled ­materials / recycling of building parts 4 The Welpeloo Residence, ­Enschede, 2012, Superuse ­Architecture: Sixty percent of the building consists of locally available recycled materials or materials ­intended for other purposes. The timber used in the facade was reclaimed from old cable drums while the glass elements are made of off- 4 cuts obtained from a nearby glass factory. 5 The ‘Lesezeichen Salbke’ openair library, Magdeburg, 2009, KARO* Architects: This structure re-uses facade elements from the Horten department store in Hamm, which was built in 1966 and demolished in 2007.

5

WASTE AND RECYCLING Many materials are already part of a closed cycle, which means that they are not declared as waste, but are processed into a secondary raw material, or used as fuel for the generation of energy. Bricks are crushed to make ­recycling concrete, glass is processed to produce insulation material, and the mineral material from demolished walls is used to make ballast for roads. The intention is to create cycles of this kind for all building materials in the future. The direct re-use of building materials is rare, because in many instances it is not possible to provide the required long-term guarantees. Only products of high artistic or historical value qualify for direct re-use. The use of second-hand materials in the repair or refurbishment of historic buildings is common; a good example is the re-use of old oak timber for the repair of historic timber framing or roof structures. The re-use of weather-resistant second-hand timber from old barns and farmhouses for ­facade cladding is also increasingly popular. Recycling with unorthodox materials such as industrial offcuts or

 4 and the re-use of scrap to form complete buildings expressive facade elements in a new function  5 gives the effect of old, familiar materials with a new and interesting feel. Whether a second-hand component can be re-used depends on a number of factors. Clearly, easy ­removal and good durability of the material increase the chances of the product’s re-usability. Another important aspect is how easy it is to separate different materials. Composite materials such as aluminium panels with foam infill are highly questionable in this context, as is thermal insulation bonded to a carrier material. It would be easy to recycle the metal profiles of a frame-based facade if the type of alloy were known and had been manufactured with a view to being recycled. This type of recycling should be made possible by the respective industry. The facade thus becomes an ecological interface, because the selection of building materials and of insulation, as well as the subsequent expenditure, all affect the energy balance and, at the same time, the choice of material determines the basic materials that are later available to waste management.

44  Fundamentals

O U T LOOK

In recent decades, the construction and technology of building envelopes has undergone rapid development. What started off as a simple transparent screen of animal skins, or a solid, monolithic wall with window openings that were limited in size, has developed into a complex component. The building envelope – facade and roof – should not be understood as an independent technical component with all its individual elements, but as an integral part of the design, as the interface between the interior and the exterior, as that part of the building which represents its ‘face’. Irrespective of the technical construction of a facade, the performance aspects are becoming more important: the catalytic properties, acoustic properties, energy generation, information transfer etc. There are no limits to its development. Research pro­jects on material properties and compound materials, as well as the knowledge gained from biology and the natural raw material resources, are yielding ever new findings. Adaptable climate envelopes – also referred to as intelligent facades – change configuration independently in a rapid reaction to the changes from day to night and from summer to winter. In the field of thermal insulation, technical progress lies in the optimisation of material properties. The growing demand for facade surfaces that can be supplied in transparent and opaque variants and the need to make use of existing solar irradiation has led to innovations such as transparent thermal insulation (TTI). Translucent filler ­materials or an aerogel developed for space travel generate the opaque effect and function as good thermal ­insulators. A facade can also be utilised for the active ­exploitation of solar energy, functioning as an energy generation and storage system. PCM modules (PCM = phase-change material) provide ­latent storage mass – in the form of hydrated salt or wax – and store solar energy which otherwise would lead to overheating. They can give off the heat via phase change during the cooler night hours as part of a closed charging and discharging cycle. The term ‘building-integrated photovoltaics’ refers to photovoltaic elements that have been installed as an integral part of a facade, fulfilling functional, energy-related and aesthetic criteria. The aesthetic requirement and the desire to integrate solar cells and collectors into the building envelope as a fully comprehensive system call for new facade solutions. At the same time, new production methods enable different dimensions and more compact component assemblies. Surface coating on insulating glazing or the integration of light control systems in the gas-filled interpane

cavity regulate the provision of daylight or shading. ­Liquid crystals and electrochromic glazing mechanically change their aggregate state and colouring in favour of transparency or opaqueness. Cleverly designed material layers can significantly reduce the energy consumption of a building. In the case of a closed cavity facade (CCF), the air gap between the ­inner insulating glazing and the outer single glazing is completely sealed. The constant passage of dry, clean air through it prevents the formation of condensate and ­increases the thermal and sound insulation properties of the elements. In addition it is possible to integrate solar screening, information systems, or lighting, for example, in the cavity. New properties of materials are being discovered with the help of computer-aided modelling and simulation, and through the analysis of Nature and its structures. The resulting composite materials and construction principles (e.g. the opening and closing of the petals of a flower) are applied to facades to create intelligent shading systems which react to changes in the climate without complex programming. Many of these experimental facades, which are currently being developed as pilot projects in research institutions, have yet to be tested for their practical feasibility. ‘Fit for the future’ does not necessarily mean high-tech. The focus on eco-balance, service life and fitness for purpose has also led to the development of facades with low technical input which make careful use of resources or use renewable materials. One example is Ricola’s new herb warehouse in Laufen, which includes an 80 metrelong solid clay facade that was constructed on site. The building manages completely without air-conditioning. The clay envelope, which has been left unplastered on the inside, is sufficient to regulate the heat and humidity within the building. The high-bay store built for Alnatura in Lorsch features a full timber construction sunk into the cooling earth, which reduces the need for air-con­ ditioning. In the case of office buildings, glass facades are being superseded by solid perforated facades, thus avoiding the need for high-tech installations; an example is the office building 2226 in Lustenau, which has a ­facade of brickwork that is 76 cm thick. This in turn consists of a 38 cm inner skin of loadbearing bricks with vertical perforations and 38 cm of insulating bricks with a greater proportion of internal air cavities. Here too, this material has made it possible to omit a large part of the air-conditioning installations normally used in office buildings. Because of the thickness of the wall, it was possible to use the masonry units without a thermal sandwich insulation system.

OUTLOOK  45

1 Office building, Rotkreuz, 2011, Burkhart und Partner: The efficient loadbearing structure and the innovative facade concept are the dominating characteristics of this office tower block. The ‘closed cavity’ ­facade consists of individually ­enclosed elements providing good thermal insulation, maximum transparency and good sound insulation; the cleaning costs are low, the solar screening is maintenance-free and the installation time was short. 2 The Alnatura high-bay store, Lorsch, 2014, BFK Architects: The ecological principles of the organic food chain were incorporated in the construction of its new high-bay store, which is currently the largest of its kind to be built of timber. The use of approx. 2,000 tonnes of PEFC-certified timber is not the only innovation; the design also dispenses with mechanical ventilation and artificial cooling by utilising simple physical effects and natural earth cooling.

1

2

3 Apartment block for IBA, ­Hamburg, 2013, zillerplus ­Architects and Town Planners: ­Photovoltaic and solar thermal panels are used as balcony railings and roof parapets in an integrated design concept. The facade element with plant growth provides thermal protection in summer, and a curtain of PCM (phase-change material) withdraws excess heat from the ­interior during the day and releases it at night. 4 Office building 2226, Lustenau, 2013, Baumschlager Eberle: The building does not need any heating system, relying solely on the heat generated by the users and emitted by the technical infrastructure in the building. The external walls consist of an inner, 38 cm thick leaf of loadbearing perforated bricks and another 38 cm thick leaf of insulating bricks with a larger proportion of perforations.

3

5 The Ricola herb warehouse, Laufen, 2014, Herzog de Meuron: Locally available natural mineral material – clay from the Laufen ­valley – was used for the new herb warehouse. The facade blocks were produced from clay in a new process in a temporarily constructed production building, and then ­installed as prefabricated elements on the site. The temperature and humidity inside the building are self-regulating. 5

4

ENCLOS E | B UIL D SEL F-SUPP ORTING ENVELOPES

Chapter 2

Introduction

48

Masonry

50

CONCRE T E

54

TIMB ER

58

48  SELF-SUPPORTING ENVELOPES

IN T ROD U CTION

The term ‘self-supporting envelope’ is used here to refer to building envelopes that consist of a solid material, such as masonry or timber, which forms both the external wall and the loadbearing structure. This type of construction is one of the traditional building methods, as are the skeleton construction systems used in timber framing. The typological distinction between self-supporting envelopes and detached, suspended facade ­elements developed during the 19th century as the result of new design ideas, materials and technologies, as well as increasingly complex requirements and building standards. The latter, in particular, mean that exposed solid constructions present us with new challenges when they have to be dealt with as part of the repair or conversion of existing buildings. In this situation, issues of thermal insulation, building physics and weather protection have to be resolved while maintaining the architectural quality. The ease of building with solid construction methods contributes to their continued popularity, primarily in residential developments. Self-supporting envelopes and wall constructions in masonry, concrete, or timber continue to be widely used, but the traditional construction materials often require some form of strengthening to allow their continued use. Historic buildings were often constructed using whatever material was available locally; one might say that they grew out of their surroundings. This very direct interaction and the properties of the material concerned led to a very natural and regional style.  1 Today, the choice of building material is almost arbitrary everywhere; nevertheless, the existence of historic buildings creates regional references which can either be

i­gnored or deliberately replicated in the conceptual design of new buildings. Solid constructions are subdivided into two categories, reflecting their structure and function: those of single-skin and multi-skin external walls. Single-skin constructions are further subdivided into single and multiple-layer systems, the latter of which perform the functions of structural support, insulation and weather protection in different layers of appropriate size and sequence. As a rule, single-skin materials consist of one single material, such as natural stone or concrete. The vigorous, homogeneous expression of such materi 3a, b als can give a building the desired appearance. However, when it comes to the current requirements, single-skin buildings are mostly no longer entirely suitable in respect of thermal insulation, moisture protection and sound insulation. By contrast, multi-skin constructions consist of a homogeneous loadbearing layer and additional elements which perform specific functions, such as the external render which provides weather protec 3c, d tion. Multi-skin constructions consist of several skins, which are either firmly connected to each other or self-supporting. As a rule, loads are supported by the inner skin while the exterior skin – with or without an air gap – has to ­satisfy the building physics requirements.  4 One example of multi-skin wall construction is a loadbearing ­masonry wall with an outer skin of facing brick and a cavity containing a moisture-resistant thermal insulation layer. Another example is a solid timber construction consisting of log planks or cross-laminated timber panels, in which the insulation layer is placed between the vertical supports and the air- and vapour-tightness is achieved

1 Historic residential building in Florence, 17th century: The external walls consist of continuous solid brickwork with a thickness of up to 52 cm. Openings give the wall a compositional rhythm.

1

2

2 Apartment building in Munich, 2014, zillerplus Architects and Town Planners: Increasing the ­density of the inner city with a building in timber construction; ­nail-laminated board has been used for the ­external walls.

INTRODUCTION  49

3a

b

3 Single-skin solid wall ­construction a Single-skin – natural stone b Single-skin – fair-faced concrete c Multiple-skin – log construction, insulated, with interior lining d Multiple-skin – masonry, with ­exterior render / interior plaster 4 Multiple-skin solid wall ­ onstruction c a Multiple-skin lightweight construction consisting of laminated wood panels with insulating layer between the panels, external breather paper and cladding b Multiple-skin solid construction, loadbearing layer, insulation and weatherproof render c Multiple-skin solid construction, loadbearing layer, insulation, air gap and facing

c

d

4a

by separate layers. The material for construction of the external wall is selected in accordance with criteria of style, function and availability. Depending on the material – masonry, concrete, or timber – different loadbearing capacities and building physics properties have to be considered. A common aspect of all solid wall constructions that function as protective building envelopes is that, in ad­ dition to the loadbearing function (the material’s own weight and that of other building components, as well as imposed loads) and the bracing function, building physics requirements also have to be fulfilled. In addition to thermal insulation, air-tightness and sound insulation, these include weathering from solar radiation, rain and frost. Crucial to the weatherproofing of facades is their protection against driving rain. The term ‘driving rain’ ­refers to wind-driven precipitation which impacts horizontally on exterior surfaces. This can lead to water penetrating the exterior wall due to the capillary properties of the building material, gravity and wind pressure. In solid types of wall construction it is important that the amount of water penetration is kept to a minimum – additionally supported by hydrophobic treatment – but also that any water that has penetrated the fabric can rapidly dry out again. Among the traditional materials in solid construction that comply with this requirement are bricks and log planks. Another common construction principle involves a loadbearing skin and an external weathering skin, separated by an air gap. In this construction the internal, loadbearing skin is protected because the outer skin, like an umbrella, keeps rainwater away from it.  4c In addition to protection against driving rain, a facade must provide adequate thermal insulation and air-tightness. For

b

c

this reason, loadbearing structures without a facing layer either feature an insulation element at their core, or internal insulation – alternatively they may be uninsulated but have significantly thicker components. Solid constructions consisting of a special material such as highly insulating bricks, aerated concrete blocks and insulating concrete, fulfil the thermal insulation requirements but (with the exception of the insulating concrete) cannot be left unfinished: they have to be rendered / plastered on both faces. In the case of insulating concrete, the insulation is applied to the core of the structure, leaving a concrete surface exposed both inside and out. Face masonry – whether of natural stone or bricks – is exposed to moisture, both rising from the ground and from rain, which enters the capillaries of the structure. Another problem associated with the masonry of existing buildings that have little or no insulation is that the surface temperature of external walls may be quite low on the inside and lead to the formation of condensate. Today, the most frequently used self-supporting construction, taking cost efficiency into account, is a solid masonry wall consisting of fired or unfired masonry units in combination with an external thermal sandwich insulation system. From a design point of view, it is important to ensure – for example, when carrying out repair work – that the special features of an existing facade, such as recesses and other decorative elements, are not covered over but replicated in an appropriate manner. This applies in particular to buildings listed as historic monuments or those in a conservation area. Ultimately however, the question arises as to whether a thermal insulation sandwich system should not be classed as a separate suspended ­facade.

50  SELF-SUPPORTING ENVELOPES

MASONRY

Masonry in its various forms has been shaping the appearance of our towns and landscapes since their creation. Initially, natural stone was used ‘as found’; it was not until the Bronze Age, when better tools became available, that the processing of stones developed. In parallel, the first clay bricks were made, which initially were left unfired. Solid masonry represents an archetypal construction method, the jointing principle of which even children playfully discover. The layering of units and permanent fastening with the help of the respective binding agent creates loadbearing systems referred to as ‘bonds’. The structural properties of masonry include high compressive strength in combination with low tensile and flexural strength. Even though the material is available today as an industrial mass product, and automated production processes are available, masonry structures are almost exclusively built using manual techniques according to craft rules. The properties of the masonry unit, its colour and structure, its shape and surface and the method of jointing give each masonry facade an individual appearance. The craft-based and technical possibilities for making openings add further variation in terms of the latter’s shape and size. The term ‘masonry’ refers to any building component constructed using natural or man-made masonry units. ‘Natural stone’ refers to sedimentary rock such as limestone and sandstone, or igneous rock such as gneiss, granite and porphyry. The category of man-made masonry units includes bricks (air-dried or fired, made of clay or brickearth), calcium silicate units and all blocks made of one or more different base materials. MAN-MADE MASONRY UNITS Bricks consist of a fired ceramic building material and can be subdivided into solid and perforated bricks. Solid bricks are the oldest type of small-format brick. They include face bricks and clinker. These are both very durable facade materials and are preferred in many regions in Europe. The appearance and colour of bricks is largely determined by the local raw material and the method and temperature of the firing. The firing and the material not only affect the strength of the unit, but also its surface and texture. For example, if the clay contains a high proportion of iron, this will turn to iron oxide during firing and give the bricks an orange-red to red colour. The colour can be varied by adding other metals to the clay mixture. For normal brick firing, a temperature of between approx. 800 and 1000° is required; from approx. 1200° the clay starts to melt (sintering). This will produce bricks with few capillaries and better hydrophobic properties. In addition, the surface is more varied, with the colouring varying from red to blue through to black and even green. The low ­water absorption ensures that these bricks have better

frost-resistance. It is almost impossible to control the colouring of the bricks in different firings, even with modern furnaces. Sorting the bricks several times results in comparable batches. The category of unfired man-made masonry units in- 1a cludes calcium silicate units, lightweight concrete blocks, concrete blocks and aerated concrete blocks. Calcium silicate units have a high raw density, which results in good sound insulation and high strength. They can be used for face masonry. Such walls are usually finished with coloured slurry or a paint coating that leaves the structure of the masonry bond visible. The finishing coat b provides extra protection to the surface of the wall and the contrast between the dark joint and the almost-white masonry unit is eliminated. Large-format calcium silicate units – referred to as precision blocks – are cost-efficient to lay. However, they are not designed for use as a face material but are normally either rendered or clad. NATURAL STONE Natural stone is used in accordance with its geological origin and its associated individual properties. It requires great manual skill to build high, structurally sound walls using stone that is unworked or merely split. Walls built of natural stone, whether ‘dry-stone’ or jointed with mortar, are perceived nowadays as an archaic form of construction. For millennia, such stones were generally used in places close to where they were found. Natural stone was always the material used for prestigious buildings such as places of worship, temples, churches and castles. Since Vitruvius, the less natural stonework exhibites the traces of processing, the greater its artistic worth has been considered. Today natural stone as a solid building material is only used in exceptional cases, ­except for the repair of historic buildings. The material is mostly used in the form of suspended slabs with back-ventila p. 86, Natural Stone tion. FORMATS AND BONDS Irrespective of whether the bricks themselves are airdried or fired, the forms that have developed all over the world are usually rectangular or square on plan and of a size and thickness that allows easy handling on the construction site. Where bricks are used as face material, these formats determine the appearance of the facade – the production process is thus visually expressed. Standardisation and serial production made bricks a ubiquitously available construction material throughout the Roman Empire. Present-day brick dimensions are based on a dimensional unit which is derived by dividing the standard measure of length by 8 (metric: 1 m/8 = 12.5 cm; imperial: 1 yard/8 = 41/2 inches). The classic

c

d

e

1 Types of masonry material a Face brick – hand-made b Face brick – machine-made c Calcium silicate block d Autoclaved aerated concrete block e Natural stone, shown as quarried block / polished panel

MASONRY  51

2 Formats and dimensions of ­masonry units to DIN 4172 – ­Modular Coordination in Building Construction a DF (thin format) b NF (standard format) c 2 DF (thin format) d 8 DF (thin format)

11,5 5,2

a

11,5 7,1

b

24,0

24,0

2

d 24,0

3 Course dimensions and header /  stretcher bonds a Header course b Stretcher course c Perpendicular joint (10 mm) d Horizontal joint (10 to 12 mm) e Face of header (brick + joint = 12.5 cm)

23,8

11,5 24,0

c

11,3 0001 1000 24,0

The dimensions and construction of masonry buildings are defined in Eurocode 6, which comprises the standards DIN EN 1996-1-1 to 3 and the respective national appendices (in Germany, this is applicable as an alternative to DIN 1053-1).

c

b

005 500

d

a

4 Brick/block bonds a Stretcher bond – all courses are laid as stretchers, with the bricks being offset by 1/2 to a 1/4 length from course to course. b Header bond – all courses are laid as headers with bricks being offset by 1/2 width from course to course. c English bond – header and stretcher courses are laid alternately. The perpendicular joints of all stretcher courses are vertically in line. d Flemish bond – header and stretcher courses are laid alternately, with every other stretcher course offset by 1/2 length from the previous one.

057 750

c

e 052 250

d

0 0

8 DF

2 DF

5 Examples of decorative bonds

NF

3

4a

b

c

d

DF

5

brick format also determines the vertical dimension of the units. For the thin format (German DF), this is cal­ culated as a multiple of the nominal brick height plus the thickness of the horizontal joint as follows (metric: thin format = 52 mm plus 1 horizontal joint × 4 layers = 250 mm; imperial: 65 mm plus 1 horizontal joint × 4 layers = 300 mm). For the standard format (German NF) it is calculated as follows (metric: standard format = 71 mm plus 1 horizontal joint × 3 layers = 250 mm; imperial: 73 mm plus 1 horizontal joint × 3 layers = 250 mm).  2 0001 The selection of brick format is determined by design aspects, cost efficiency and the work process. The smaller formats are usually better suited for use as face brickpiers, lintels and for walls that are curved on plan. 05work, 7 By contrast, the larger formats are primarily intended for more efficient work processes and are particularly economical for use in internal and external walls with large 005 areas. In addition to the size and colour of the brick, it is the way in which courses are laid – the bond – that determines the appearance of face brickwork. The two basic 052 courses of brickwork are the header course (with the end of the brick showing) and the stretcher course (with the  3 side of the brick showing). 0 By arranging the courses in different ways or offset from each other, different bonds are created, such as the header bond in which only the heads of the bricks are visible, or the English bond in which a header course follows a stretcher course.  4 Beyond these basic examples of bonds, a wide range of other bonds exist. In addition, the architectural effect can be enhanced by projecting or receding courses, which have a sculptural effect on the facade. Brick bonds lead to a strict, ­almost mathematical system of rules for the design and construction of facades. The art lies in straightforward, natural arrangements and jointing in harmony with the overall appearance.  5

52  SELF-SUPPORTING ENVELOPES

Joints In addition to the masonry units, it is the joints that give character to masonry. A distinction is made between horizontal joints – the horizontal connection between the upper and lower faces of the brick courses – and the perpendicular joints, the vertical joints between the heads of the bricks. The type of mortar and thickness of the horizontal joint, as well as the ratio between joint width and joint depth, all depend on the format of the masonry unit used. For common brick formats (e.g. DF or NF), the mortar thickness in horizontal joints is approx. 12 mm (imperial: 10 mm) of standard mortar whereas precision blocks such as those of calcium silicate, aerated concrete or ­cement-based material are bonded using thin-bed mortar (approx. 2 mm thick). The design of the joints is important both for their effect and, primarily, for their durabil 1 Similarly to the masonry units it holds together, ity. the joint material has to fulfil demanding requirements with regard to air-tightness, protection against driving rain and durability. The greater thermal conductivity of the joint material compared to the masonry units must be considered in the energy balance, as it is a potential thermal bridge. The simplest and most economic joint face is created with a ‘flush joint’, in which the gap between masonry units is fully filled with mortar and any protruding material is struck off flush with the trowel. The colour of the mortar determines the colour of the joint, the wall mortar being the joint mortar. Where the joints are fully filled subsequently, the mortar is removed to a depth of at least 1.5 cm and the facade is pointed up, filling the empty part of the joint with a facing mortar in a separate work process. In this way it is easier to control the intended visual

effect, since it is easier to inspect the colour of the mortar and to achieve different forms of joint facing. SURFACE STRUCTURE The external layer of material works as weather protection as well as performing an aesthetic function. The ­appearance of the facade can be significantly influenced by either emphasising the joints and the joint pattern or understating them, with the design options ranging from sober functionalism to ornamental whimsy. With respect to the colour scheme of facades, the following rule of thumb applies: the darker the colour of the joint, the more radiant the appearance of the masonry unit. Another design option is the use of what is known as a decorative bond. A special expression can be achieved by using an irregular pattern, a special pattern or ornamentation that has been designed in detail and specified in a laying plan. In addition, the colour scheme of the bricks used can be modified either by sorting the batches delivered, or by mixing additives into the joint mortar. A plain rendered area can be textured by using different rendering methods and materials, as well as by adding granulate or pigment to the mortar. OPENINGS In solid, self-supporting masonry, the size and shape of openings is limited for structural reasons, also affecting the potential number of windows. In the past, horizontal supports between uprights were built with brick arches, whereas today they are created using concealed lintels of steel or reinforced concrete.  SCALE, vol. 1, Open | Close The craft-based, classic methods of building openings in masonry depend on the material, with openings forming

1a

b

c

d

e 1 Different options for finishing joints a Concave joint b Flush joint c Weather joint d Repointed joint, the joint has been raked out and filled with new mortar e Struck joint, providing poor protection against water ingress

2 Refurbishment of factory building, Munich, 2004, Allmann Sattler Wappner Architects: The listed rear building dating from 1893 has been fully refurbished. The special effect of the masonry with face bricks in the historic format of 25 cm × 12 cm × 6.5 cm is created by applying a lime wash finish. 3 House extension, Aachen, 2011 Amunt Architects: The brick facade of the existing building is keyed into the extension wall consisting of light-weight pumice / concrete blocks, which – with a thickness of 24 cm and good thermal insulation properties – reduce trans­ mission heat loss. This contem­ porary ­approach plays off the different ­colouring of the new and old masonry against the compact form of the new building. 1 + 1 = 1. 2

3

MASONRY  53

an important design element that can become an ornament in the facade. SOLID MASONRY Today, solid masonry structures with solid bricks or clinkers as face brickwork can only be used for unheated utility buildings. Face brickwork structures which comply with the current requirements for thermal insulation consist of highly insulated masonry units made of porous clay or aerated concrete. The masonry courses are bonded with a polymer-modified mortar and the perpendicular joints are tongue-and-grooved. This means that the exterior walls have to be rendered/plastered on the outside and inside in order to ensure air-tightness and protection against rainwater. Lintels, wall connections and the support of floor slabs require detailed design, since specially shaped units are required in order to minimise thermal bridging and to comply with the requirements for sound insulation and structural integrity. With this type of construction and appropriate wall thicknesses, it is possible to achieve good U-values without having to forego the advantages of a solid construction. When it is intended to achieve the visual effect of face brickwork, it is also possible to consider a special skin of face brickwork, in which the masonry looks very similar to a solid masonry wall, but has the advantage of complying with the requirements for thermal insulation and protection against the  p. 82 ff, Face Brickwork and Brick Panels weather. Special attention needs to be paid to the selection of the render/plaster systems, which must be suitable for the material properties of the masonry unit used and which are part of the entire wall system.

b

a

c

a

4 Section through masonry wall construction, scale 1:20: a Wall construction: Clinker face brick, 140 mm Narrow gap, thermal insulation, 115 mm Loadbearing masonry, 240 mm Internal plaster, 20 mm b Roof construction: Layer of gravel, 50 mm Double layer of bituminous sealing membrane Insulation with a fall, 200 to 300 mm Bituminous vapour barrier Reinforced concrete slab, 160 mm, with plaster finish, 15 mm c Construction of ground /  upper floors: Solid wood planks, 23 mm Floating screed, 40 mm Separating layer Impact sound insulation, 30 mm Reinforced concrete floor slab, 150 mm

c

4

54  SELF-SUPPORTING ENVELOPES

CONCRE T E

Concrete is a construction material that consists of a mixture of cement, water and mineral aggregate. It cures and takes the shape of the formwork holding it. Knowledge of this material and its properties has existed since the second century BC: it was called opus caementitium by the Romans. It was not until the end of the 19th century, when steel began to be used for reinforcing concrete, that this ­material was able to support greater structural loads and hence became widely used in building construction, even creating a specific construction style. In its uncured state, concrete can easily be shaped and is therefore very suitable for the sculptural design of facades involving large spans. The material, which is constantly under­going further development, is very cost-efficient and offers great design flexibility with regard to shape, treatment and surface finish, making it a very popular material. Concrete can be adapted to meet many different requirements whether they relate to structural strength, durability, building physics, fire protection or specific user needs. Designs should avoid subjecting it to changes in shape due to temperature fluctuations, and to the ingress of water, both of which have a negative impact on the properties of concrete. Concrete is either mixed on the construction site – referred to as ‘in situ concrete’ – or transported to the site in ready-mixed liquid form, which is then pumped directly into the formwork and compacted. It is also possible to supply the material to the construction site in the form of a prefabricated or semi-prefabricated element, which is placed by crane. In view of current requirements regarding thermal insulation and for the avoidance of thermal bridges, it is not possible to have monolithic exterior walls unless they are

2

very thick, even if insulating concrete is used. For this reason, concrete building envelopes are normally built using a two-skin construction with core insulation or suspended, prefabricated, concrete facade panels. It is also possible to build solid concrete walls with interior insulation; in this case (and in contrast to exterior core insulation) it is important to minimise any thermal bridging via components that connect with the exterior skin of the wall (i.e. floor slabs and interior walls). Production In addition to the basic ingredients, i.e. cement, aggregate and water, it is possible to use various supplementary cementing materials and chemical admixtures to modify the properties of the concrete. Adding materials such as stone dust or pigments affects the colour of the concrete, while glass fibres or plastic fibres improve its loadbearing capacity. Concrete additives are only used in small quantities, but they change the chemical and physical effect of certain properties of the fresh, uncured concrete, without it losing its durability and without the steel losing its corrosion protection. For example, plasticiser changes the workability of concrete. The strength of concrete and its consistency during processing depend on the proportion of its constituting components. The choice of stone dust and the size of grain affect the appearance and strength of the material, as do the quantity of additives and the compatibility of different additives. The quality of concrete is affected by the water / cement ratio (w /c ratio). The strength of concrete is reduced when it contains too much water. The consistency of concrete, which here refers to its stiffness, depends on the purpose it is to be used for. For the purpose of laying concrete, it is important to ensure that it can be put

3

1 Constituents of ­concrete (see DIN EN 206 Concrete) Cement – CEM I: Portland cement – CEM II: Portland composite ­cement – CEM III: blast-furnace cement – CEM IV: pozzolanic cement – CEM V: composite cement Aggregate (types) – fine, naturally rounded (sand / crushed stone fines) – mixed grain (gravel / stone chips) – coarse, broken grain (coarse gravel, crushed stone) Water – gauging water – surface moisture Concrete admixtures used to change the properties Fine mineral material: – stone dust – fly ash, ground tuff, trass or ­silicate Organic substances: – synthetic resin emulsions Others: – colour pigments – fibres (steel, glass, or plastic) Concrete admixtures for modifying the physical and / or chemical properties, such as: – workability – curing behaviour – hardening – durability in the form of plasticisers, retarding agents, accelerators, stabilisers and waterproofing agents. 2 Unité d’Habitation, Marseilles 1947–1952, Le Corbusier: The coarse, rough finish of the ­untreated concrete is elevated to an aesthetic feature. The bétonbrut is treated like stone and benefits from the contrast with the surfaces of the other materials, such as steel and glass, and the colours used on the loggias and sill panels. The concrete was installed without any insulation, owing to the mild ­local climate and the lack of energy-­saving regulations at the time. 3 L 40, Berlin, 2010, Roger ­Bundschuh, Cosima von Bonin: The forms are accentuated by the envelope of black face concrete without joints. The solid ­facade consists of three layers – a loadbearing inner layer of in-situ concrete, core insulation and an outer skin of lightweight concrete with black pigment.

CONCRETE  55

4

CONCRETE TYPES

DESCRIBED in TERMS of THE MANUFACTURING PROCESS, INSTALLATION METHOD AND PROPERTIES

Top concrete

Concrete which is added subsequently to an existing concrete layer, e.g. in order to make up the level or to improve the loadbearing capacity.

Prefabricated concrete ­elements

Concrete, reinforced concrete, or pre-stressed concrete components ­prefabricated in a factory, which are installed on site fully cured.

Insulating concrete

Special form of lightweight concrete with foam glass instead of stone aggregate to give it good insulation properties.

Fibre concrete

Concrete with an admixture of fibres (steel, glass, or plastic) in order to improve the mechanical and structural properties.

High-performance concrete

Concrete with high compressive strength, achieved by minimising the water / cement ratio; this is used for compound structures and special structures of ­minimal dimensions.

Lightweight concrete, autoclaved aerated ­concrete

The weight of this concrete is reduced by omitting stone aggregate and aerating the concrete. Low thermal conductivity.

Standard concrete

Concrete which is compacted by vibration and achieves its final compressive strength after 28 days; av. strength class C25/30; may include various additives.

In-situ concrete

Concrete made and used on site; it is compacted and cures in the formwork. The concrete can be strengthened with reinforcement steel in order to improve its structural performance.

Recycling concrete

Concrete in which the stone aggregate consists of recycled concrete and crushed masonry.

Reinforced concrete

Compound material of concrete and steel. The partial strengthening (reinforcement) of concrete results from combining its high compressive strength with the high tensile strength of steel.

Rammed concrete

Concrete without reinforcement, which is compacted in layers by ramming (or tamping) instead of vibration.

Fair-faced concrete

Concrete with specific requirements for its visible surface. The surface texture can be modified by using special formwork surfaces, surface treatment and ­additives such as colour pigments.

Ready-mix concrete

This concrete is mixed at a central location and transported to the site.

in place and compacted without difficulty; possible consistencies range from very stiff to very free-flowing and include self-compacting concrete (SCC). When pouring concrete into the formwork, it is important to ensure that the mixture does not separate. It should be compacted evenly to prevent air inclusions. Similarly, a constant ­external temperature is important during installation, preferably between +5 °C and +30 °C, otherwise suitable measures must be taken to maintain the material’s workability, e.g. cooling and the addition of water when the ambient temperature is too high. The required compressive strength is normally reached after 28 days of curing. In order to give the concrete its form it is poured into hollow formwork (shuttering). This consists of a formwork system (dependent on – or independent of – the building, made of timber, steel or plastic) to which sheathing is fixed (form face creates surface texture). Shuttering ties consisting of threaded bars with screw anchors in a conduit are used to prevent the hollow formwork being pushed apart. The anchor holes remain visible after curing, and are closed with a plug after curing. For this reason, the arrangement of the anchors should be considered as early as the design stage. JOINTS When building with fair-faced concrete, attention must be paid to joints on account of their visibility, be they shutter­ing joints, day-work / construction joints, required ­expansion joints, or dummy joints designed for appearances. The design of the joints is a critical aspect, whether it is intended to give the building component a smooth appearance, or impose, for example, a grid pattern. Narrow joints with little or no surface gap convey the impression of a smooth surface whereas broad joints with a pronounced surface gap emphasise the impression of individual panels due to the effect of the shadow. In addition to appearances, the format of concrete panels and even concrete components must take into ­account technical requirements relating to production; the size of panels is restricted by their weight and the ­options for transporting them.

4 Concrete terms 5 Joint details The width of the joint and the thickness of the jointing material depend on the size of the elements: the ­expected movement due to thermal factors must be absorbed in the joint. Such joints are usually 15 to 20 mm wide. > DIN 18540 a Joint sealer (joint sealing compound and foam strip) 5a b Joint with plastic compression profile c Dummy joint, design element

b

c

6 Consistency check 7 Installing a formwork anchor 8 This climbing formwork consists of large shuttering panels which are pulled upwards at regular intervals once the concrete has cured. 9 Formwork system for loadbearing walls; large formwork elements that are placed in sections using a crane

6

7

8

9

56  SELF-SUPPORTING ENVELOPES

Fair-faced concrete Fair-faced concrete refers to concrete components with a surface that remains visible; their appearance is normally determined by the texture of the form face. Fairfaced concrete is defined according to a range of classes.

consisting of wood-based materials with different types of plastic coating are a popular choice. The use of such panels produces very smooth surfaces; the texture of the facade is determined by the pattern of the panels (i.e. the joints) and the fixing anchors. The tighter the formwork is, the better it prevents the run-off of the cement slurry when the concrete is placed and compacted. This reduces unwanted defects in the colour, surface pattern and texture. Release agent is applied to the formwork before the concrete is placed and ensures that the formwork can be easily released from the component after curing. Nevertheless, the removal of the formwork can be a difficult, labour-intensive process – similar to the design and construction of the formwork, for example in the case of complicated shapes with several curved surfaces. Of special significance in concrete components are the edges. These are usually formed with a chamfer (which is created by inserting a small triangular batten into the formwork) in order to avoid damage to the edge during the construction process or at a later date. Should any breakage occur to a sharp edge, i.e. one without any chamfer, this can only be repaired manually. The points of repair are usually visible due to differences in colour, which may become more obvious as the material ages.

 1

The quality of fair-faced concrete can be assessed objectively with the help of DIN 18217 ‘Concrete surfaces and formwork surface’ or SIA 118/262 ‘General conditions of concrete construction’. FORMWORK SURFACE – TEXTURE The surface of concrete elements can be modified using various methods of texturing the surface as described below. One of the means of doing this is the shuttering, the inner surface of which is particularly important as it is the negative form of the concrete component it is meant to create. When the shell construction is designed, a formwork plan is an important design element, defining the geometry of the formwork and the desired joint pattern. Once the concrete has cured and the formwork or shuttering has been removed, its profile and texture can be seen on the surface of the concrete element. The appearance can be affected by the choice of different formwork materials, different sizes of shuttering panel and the layout of the fixing points. The quality of the surface appearance is subdivided into fair-faced concrete classes on the basis of criteria for the formwork skin, the expansion joints and joints in the formwork, porosity, evenness of colour and smoothness of the surface. In view of the fact that the requirements are very exacting, it is important that all those involved in the design process are consulted in good time and that the tender documents include a specific description of the design. Similarly, it is a good idea to produce sample surfaces to define the texture and quality of the finish. The successful completion of a specified finish and the quality of fair-faced concrete depend on a number of factors, such as the quality of the concrete mix and additives, the processing (soiling, leakiness of the formwork, incorrect compaction or release agent) and the effects of the weather (external temperature, precipitation). When choosing formwork / shuttering material, it is important to ensure that it does not trigger a chemical reaction with the concrete during the curing process. For this reason, preferred materials include timber and woodbased materials, steel or plastic. When timber shuttering is used, e.g. rough-sawn timber boards, the material must be soaked in water first so that it does not start swelling when the concrete is poured in, as this would withdraw too much water from the concrete and would result in sanding of the surface after curing. Shuttering panels

2

3

Standard concrete

Lightweight concrete

Dry bulk density

2000–2600 kg/m3

350–2000 kg/m3

Compressive strength

5–55 N/mm2

2–6 N/mm2

Strength classes

C8/10 to C50/55

LC8/9 to LC50/55

Thermal ­conductivity

1.51–2.3 W/mK

from 0.11 W/mK

4

1 Fair-faced concrete classes These define the requirements for the surface, the formwork pattern and the edges. 1: low level of requirements: cellar walls or areas primarily used for ­industrial purposes 2: normal level of requirements: stairwells, retaining walls 3: special requirements: facades in building construction 4: non-standard special requirements: prestigious components in building construction

2 Comparison of properties of standard and lightweight ­concrete 3 Visitor information centre at the Messel mine, 2010, Landau + Kindel­bacher: The solid reinforced concrete building is constructed of in-situ concrete with a fair-faced concrete finish inside and outside, forming a double-skin external wall with core insulation, the work being divided into 87 sections. The texture of the walls was created by constructing the formwork with a skin of planed, tongue-and-groove boards, with an irregular arrangement of the board joints. Concrete class C25/30 to C45/55, fair-faced concrete class 2 4 Gropius’ new Meisterhaus, ­Dessau, 2014, Bruno Fioretti ­Marquez Architects: Contemporary reconstruction on the existing foundations. The external walls are built of light-coloured lightweight concrete with low thermal conductivity so as to minimise the weight on the historic foundations and avoid the need for additional insulation. The natural stone aggregate was replaced by expanded clay globules and lightweight sand in order to ­reduce the weight of the shell construction further. Concrete class LC 12/13, ­fair-faced concrete class 4

CONCRETE  57

If it is intended that the facade has a more pronounced, high-relief texture, it is possible to process the surface of the cured concrete mechanically or chemically, or to use concrete matrices to create a special effect. These matrices come in serially produced patterns but may also be tailor-made. A special application of matrices is photoengraving, in which a photographic image is transferred to a sheet material using a CNC milling machine in order to create the relief which then models the fair-faced concrete surface; another option is the direct application of photographic prints to prefabricated concrete panels for the purpose of facade decoration.

5 Surface, textures a Showing the shuttering panels and anchor points b Surface resulting from roughsawn shuttering c Visible result of the laying ­process, e.g. tamping d Relief created by inserting moulds into the formwork 6 Surface, colours a Colouring achieved with colour pigments and pulverised stone b Imprinted surface / 3D print 7 Detail of section through fairfaced concrete wall with core ­insulation, scale 1:20

b

a

COLOURING The colour of concrete is affected by the selection of the cement and aggregates. In order to achieve as homogeneous a colour as possible, the mixture (cement, aggregate size and added materials) and the water/cement ratio should be as consistent as possible. In addition, all material supplies should come from the same cement factory or aggregate supplier. Classic mixtures are likely to have a dark-grey to light-grey colour. Raw materials with low iron oxide content make it possible to produce white Portland cement, which in turn produces very pale grey concrete surfaces. It is also possible to add pigments to the concrete mixture to achieve a certain ­colour scheme. Oxide pigments can give the following colours: – white: titanium oxide – red, yellow, brown, black: iron oxide – green: oxides of cobalt, nickel, zinc, titanium and aluminium – blue: oxides of cobalt, aluminium and chrome – yellow: oxides of titanium, chrome, nickel and antimony

a Wall construction: Reinforced / in situ concrete, 250 mm as weather protection Thermal insulation, 120 mm Reinforced / in situ concrete, 250 mm as loadbearing layer b Roof construction: Concrete slabs laid in sand, 150 mm Bituminous sealing membrane, 10 mm Thermal insulation, 200 mm Bituminous membrane as a ­secondary seal, 5 mm Lattice girder plank with added concrete, 260 mm c Floor construction: Hardened screed, 20 mm Cement screed with underfloor heating, 80 mm Bituminous sealing membrane Impact sound insulation, 40 mm Fair-faced concrete floor slab, 280 mm

c

The colouring of concrete is durable and weathers well, although the intensity usually diminishes somewhat during the first years of service.

5a

c

6a

b

d

b

7

58  SELF-SUPPORTING ENVELOPES

TIMB ER

Alongside clay and natural stone, timber is one of the oldest building materials and is of paramount importance throughout the world due to its excellent structural properties and wide regional availability as a renewable raw material. Similarly to clay, timber contributes to an agreeable indoor climate because – in addition to its moistureregulating capacity – its lower thermal conductivity ­allows its surface temperature to remain similar to that of the air in the room. When designing timber-based structures, it is important to take into account the change in volume due to shrinkage and swelling of this natural material, and the additional fire protection measures ­required. Careful selection of the material and skilful ­handling, working and installation are important when choosing timber as a construction system. In solid wall construction, a distinction is made between different construction methods. One of the oldest methods of building with timber is log construction – also known as ‘strickbau’ in the Alpine region – along with the use of piles for stilt houses. In these systems entire logs are prepared and stacked, and the structure is made rigid by the jointing details at the corners (called ‘verstricken’ in the Alpine region).  1 A characteristic feature of this construction is the projection of the logs at the corner joints, which is a geometric and structural necessity. The round logs, which have been stripped of their bark, usually remain visible externally and thus determine the appearance of the building. With the help of different profiling techniques, for example by making special grooves and inserting profiles to create a secure bearing, the logs are prepared for true horizontal and structurally sound stacking. In this way the construction can be carried out without additional fasteners. Today, additional thermal insulation is added in the core of the wall, as well as an air-tightness membrane, in order to comply with current thermal insulation and air-tightness requirements. In ­contrast to modern timber frame construction, log construction has to comply with strict specifications in con-

struction and design in order to meet the necessary standard of workmanship. Settlement of several centimetres has to be taken into account, as do the openings in the facade, which are ­determined in their arrangement and size by the ‘module’ of the log. Traditionally, these buildings feature relatively large closed areas and small window openings in landscape format. The obvious material 1a jointing and its ­dimensional conditions contribute to the special, archaic attraction of such buildings. The dimensions take into ­account the naturally available length of logs which, for spans without posts, are approx. 4 to 5 m. The layout ­design is based on the rectangular positioning of the ­internal walls. Timber construction systems ­using planks glued together are a modern form of solid timber construction. In contrast to logs, these panel-type elements – which are referred to as nail-laminated and cross-laminated board – consist of largely dry and nonshrinking layers which are glued together straight, across b or cross-wise, or nailed or even doweled, and which are 1 Corner joints  5, 6 either produced as solid units or include a cavity. a Traditional round logs The ad­vantageous properties of these components are Structurally effective connection by their reduced cross-section, low weight, high strength notching the logs on one side b Square-sided logs and ­dimensional stability. The option to manufacture Structurally effective connection by such components as prefabricated elements facilitates dovetailing both contact surfaces installation on site. Since the size of panels is not sub- along both axes ject to a specific dimensional system, only the manufacturer’s specific sizes have to be taken into account. The timber material itself is often concealed, because the loadbearing elements are covered by an external layer of insulation to afford the necessary thermal protection and may also feature a separate cladding on the inside. In contrast to the classic log-built buildings, openings of any size and shape can be cut into these modern elements. This means that the facades no longer have to adhere to the strict order of log construction and allow more and larger openings, with greater flexibility in the interior layout.

2 Historic log building in Grisons The natural stone plinth serves as foundation wall, to even out the ­terrain and to protect the timber structure above it from snow and humidity

2

3

3 Timber buildings in Vrin, Gion A. Caminada: Traditional methods that have been given a technical upgrade to produce this contem­ porary expression of the ‘strickbau’ method, a Swiss variant of log ­construction that is typical of Vrin.

TIMBER  59

4 Forms of solid timber wall ­construction a Round logs with flat contact ­surfaces and fillet joints b Rectangular section logs with tongue and groove c Rectangular section logs with ridge and groove d Log wall with thermal insulation e Prefabricated units of laminated solid timber plus thermal insulation 5 Different kinds of vertical timber lamination a with square arrises b chamfered c profile with cable groove 6 Different kinds of timber ­cross-lamination a alternate layers of cross-lamination b cross-lamination with some layers in parallel with adjoining layers c cross-lamination with cavities between layers

4a

b

c

d

5a

6a

b

b

c

c

e

7 The Schattenbox residence, Eichgraben, 2008, Superlab – Dold and Hasenauer OG: The fully prefabricated cross-laminated timber units consist of solid timber sections. The cross-lamination of the different layers of the units results in good dimensional stability and structural strength. 8 Cross-section through a log ­building, scale 1:20 Wall construction: Log construction, loadbearing, 120 mm Thermal insulation on grid of ­battens as substructure, 120 mm Vapour check Thermal insulation between ­battens as installation plane, 40 mm Double layer of plasterboard, 25 mm Roof construction: Roof tiles Battens / counter-battens Rafters with thermal insulation, 180 mm Vapour check Thermal insulation with battens as ­installation plane, 40 mm Double layer of plasterboard, 25 mm

7

8

ENCLOS E | B UIL D NON SEL F-SUPP ORTING ENVELOPES

chapter 3

IN T ROD U CTION

62

M UL LION / T R ANSOM FACADE

66

GL ASS AND GL A ZING EL EMEN TS

70

EL EMENT FACADE

72

D O UB L E-SKIN FACADE

74

EL EMENT FACADE – CONCRE T E

76

EL EMENT FACADE – TIMB ER

78

Sandwich systems

80

SUSPENDED FACADE – FACE B RICK WORK

82

SUSPENDED FACADE – B RICK PANELS

85

SUSPENDED FACADE – NAT UR AL STONE

86

SUSPENDED FACADE – ME TAL

88

SUSPENDED FACADE – FIB RE- CEMENT BOARD

92

TIMB ER FACADE

94

PROFIL ED ST RU CT UR AL GL ASS AND P OLYCARBONAT E PANELS

96

MEMB R ANE FACADE

98

COMP OSIT E T HERMAL INSUL ATION SYST EM

100

62  NON SELF-SUPPORTING ENVELOPES

IN T ROD U CTION

1

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The desire for larger openings that provide more daylight and ventilation, while at the same time providing protection against the weather and changes in the climate, drives the search for new materials. Similarly, the need for larger spans and economic structures, which is a feature of the industrial age, has led to modern construction systems. Industrial methods of producing and finishing materials such as steel, glass, metal and reinforced concrete broaden the formal and technical possibilities of architecture. Industrialisation has made it possible to overcome the material heaviness of this construction system. Comparatively slender cast-iron and iron structures – initially used for smaller bridges and later for daring feats of engineering – make large spans possible. Frames with rigid nodes and frame construction constitute a secondary loadbearing structure which supplements solid construction components and opens the door to layouts with greater flexibility of use – independent of the facade and its openings. The Crystal Palace, which was designed by Sir Joseph Paxton on the occasion of the World Exhibition in London in 1851, is considered a milestone in the quest to alleviate the hea­ viness of the building envelope. Prefabricated from modular iron and glass components and constructed in a short period of time, the building represents the beginning of the glass / steel architecture of modern high-rise building construction.  1 The first facades involving this type of lightweight construction with a high proportion of glass were designed for industrial buildings. In order to improve working conditions in factories and thereby improve the performance of the workers, glazed building

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envelopes were developed as an interface between interior and exterior, admitting more daylight and sunshine and allowing an increased air exchange. In consequence of this, they surrendered their loadbearing function.  2 Ludwig Mies van der Rohe, an important proponent of the Modern movement, promoted the separation of the architectural elements according to their functions into loadbearing and non-loadbearing elements, consisting of different materials and structures. For a competition for a high-rise building in Berlin in 1921, he produced a ­design that expressed his vision of ‘skin and bones architecture’, in which the transparent glass skin encloses the loadbearing structure, which itself consists only of columns and floor slabs. Farnsworth House, which is a later design, is considered a prototype of all modern glazed buildings. The loadbearing structure consists of a slender steel skeleton construction and the frames of the facade, with its large glazing panels, are attached to the steel columns with angle profiles. This principle of enclosing a building, in which the facade encloses the primary structure like a curtain (hence the term ‘curtain wall facade’), allows flexible use of the layout, which can be zoned at will, independently of the facade. The industrial production of prefabricated elements meant that lightweight slender facade elements soon became a viable alternative to solid building envelopes. Today, curtain wall facades make an important contribution to the economical construction of buildings, particularly office and administration buildings.  3, 4 The expressive term ‘curtain wall facade’ stands for a range of technically differentiated construction systems.

1 The ‘Crystal Palace’, Great ­Exhibition, London, 1851, Sir ­Joseph Paxton: In spite of its ­ornamental embellishment, the bold glass iron construction – with the streamlined and slender loadbearing structure providing an uncluttered interior – represents the transition to modern architecture. 2 Steiff factory, Giengen, 1893: The double-skin facade consisting of translucent glass panes is considered to be the first curtain wall in industrial building. The outer ­facade has been suspended in front of the construction, while the inner one stands between the columns. 3 Bauhaus Dessau, 1926, Walter Gropius: The glass facade suspended in front of the loadbearing ske­ leton structure determines the ­appearance of the workshop wing and reveals the structural elements. The glazing at the building corners reinforces the lightweight impression. 4 The Farnsworth House, 1951, Ludwig Mies van der Rohe: The ­external walls consist of large-­ format glass panes, connecting the cubic interior with the outdoor space.

INTRODUCTION  63

For example, there is a fundamental difference in the construction of a curtain wall facade and that of a suspended facade with back ventilation. A curtain wall facade functions as a ‘warm facade’ without back ventilation – either in single-skin form as a mullion/transom facade or element facade, or as a double-skin facade. The lightweight, non-loadbearing external wall is suspended from the loadbearing structure as an independent package, either floor by floor or spanning several floors.  p. 66 ff By contrast, a suspended back-ventilated facade is termed a ‘cold facade’, which has an air space that separates the protected insulation layer from the external weathering layer. The cladding of the exterior skin is ­independent of the loadbearing structure but firmly ­attached via a substructure.  p. 82 ff In both systems many requirements have to be met by slender building components in a small space. These are complex items in terms of their construction, delivery and installation. For this reason it makes sense to involve specialist designers, system manufacturers and construction companies in the design at an early stage. CURTAIN WALL FACADES A curtain wall facade is a lightweight, non-loadbearing envelope which is attached to the loadbearing structure of the building using a substructure. The term ‘curtain wall facade’ covers the mullion /transom construction method, the element facade and the double-skin facade. A distinction is made between systems using individual framing elements and facade elements, which are attached to a skeleton structure. Both systems consist of a frame construction using storey-high mullions and horizontal transoms to produce entire shear-resistant elements. The spaces created by the framing are filled with a range of different materials with a bracing function – transparent glazed elements or opaque panels – and functional elements, such as openable windows and doors, ventilation elements, solar screening and glare-protection ­elements.

The framing is primarily constructed using steel and aluminium profiles, and occasionally also timber profiles. Sandwich elements consist of an insulating core with covering layers of plastic, glass, metal or reinforced concrete. There is a relatively wide choice when choosing the grid pattern of the facade, because the loads are transferred – either suspended or from the ground up – separately from the main loadbearing structure. The connection points of the facade to the primary system must have fixed points as well as sliding ones, in order to be able to absorb any movement from the loadbearing structure, and they must be three-dimensionally adjustable so that tolerances in the construction can be accommodated. The difference between a mullion / transom facade and an element facade consists in the degree of prefabrication. This also affects how the elements are joined, which parts of the profiles are exposed to view, and the sealing planes. Particular attention must be paid to the joint between the elements. While the mullion / transom facade, installed on site, still allows a certain freedom in the ­facade design and the adaptation of the sealing system, as well as in the finishing pressure plates, the installation of the individual elements of an element facade relies on the fixings being precisely aligned to the shell structure. The elements are placed on brackets (or the elements below) and are laterally pushed together. In this way, one installed element secures the next one, which is then ­attached to the primary system at the free ends. In this system the visible width of profiles at the joints is larger. The system is particularly attractive for large construction sites and high-rise buildings owing to prefabrication and pre-assembly of the glazing and the integration of any services installations, as well as the short installation time and potentially the possibility of working without scaffolding. A limiting factor is the restricted design freedom, since individual requirements can only be ­accommodated to a very limited extent due to the serial production of the system.

5 Curtain wall facade (suspended) 6 Mullion / transom facade built from bottom up or suspended Semi-finished products are assembled on site 7 Facade system of prefabricated units 8 Double-skin facade Building services are integrated in the respective facade system

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64  NON SELF-SUPPORTING ENVELOPES

SUSPENDED BACK-VENTILATED FACADE Suspended back-ventilated facades (DIN 18516-1) are based on the principle of double-skin construction. A loadbearing inner layer takes on the structural and sealing functions of the facade, while the outer layer, like an umbrella, protects the structure against the impact of the weather.  1 The weather skin is never watertight; it may even be designed with open joints, depending on the material. Any penetrating water will normally run down the back of the outer skin. The base of these structures and any connections to openings in the facade must ­allow the water to drain off in order to prevent damage from the ingress of water into the building fabric. An air space is formed between the skins, in which – like in a chimney – air flowing in from below rises, thereby discharging any penetrating condensate through evaporation at the top. This system can be used with a wide ­variety of cladding materials, and thus allows great freedom in the design of the facade. Compared to single-skin cladding that is attached directly to the exterior envelope, back-ventilated double-skin construction systems have the advantage that the materials can independently shrink and swell, as well as contract or expand according to fluctuations in temperature. With the correct detailing, it is possible to use non-diffusive materials, such as metal, without any negative building physics effect on the inner loadbearing part of the wall. Depending on the material of the external skin, the substructure can consist of timber battens and profiles, lightweight metal profiles, or stainless steel elements. In order to avoid stress from lack of free movement, the substructure must be able to accommodate movement in all directions. A temperature range of between –20 °C

and +80 °C must be taken into account. Substructure systems should be permanently protected against corrosion; this should include any damaging effects from ­adjacent building materials (crevice / contact corrosion). Nowadays, depending on the function of the building, back-ventilated facades are fitted with an insulation layer on the outside of the inner skin. The thermal weak point of the system is the point of attachment of the envelope to the loadbearing building component. In view of the fact that the exterior envelope of a doubleskin system is separate from the structural system of the building, it is important to pay attention to the relationship between the interior and exterior. While the pattern of joints only has an indirect relationship with the loadbearing part of the structure, the two elements nevertheless have to be designed to complement each other. The size and arrangement of openings is limited owing to the structural limitations of the loadbearing structure. Individual windows are just as possible as fenestration bands or a combination of suspended opaque facade elements with large glazed ­facade panels. An important part of the detailed design is the position of the window in relation to the insulation plane and the construction of the reveals, particularly with respect to back-ventilation and the ingress of moisture. Today, back-ventilated double-skin construction systems are used for a wide range of buildings. One reason for this is the diversity in conceptual design based on the various materials available, such as ceramics, natural stone, reconstituted stone, metal, timber, fibre-cement panels and plastic. Many suspended systems can be used for both wall cladding and roof cladding.

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1 1 Schematic of suspended, ­back-ventilated facade. a Height of coping a with fall b External skin = weather skin c Air gap, back-ventilation d Insulation e Loadbearing structure f Drip edge; its overhang depends on the building height < 8 m = a ≥ 5 cm < 20 m = a ≥ 8 cm > 20 m = a ≥ 10 cm g Water discharge

2 Examples of suspended, ­back-ventilated facades: a Student housing at Campus Westend, Frankfurt am Main, 2008, Karl + Probst Architects: The largeformat fibre-cement panels provide a structure to the facade. b The Brandhorst Museum, ­Munich, 2009, Sauerbruch Hutton: Ceramic bars with differently ­coloured glazing suspended in front of the wall let the building appear solid or airy, depending on the mood created by the changes in daylight.

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c The Riverside Museum, Glasgow, 2011, Zaha Hadid Architects: The complex geometry of the building envelope is enhanced by the material and orientation of the titanium zinc sheets.

INTRODUCTION  65

SUSPENDED FACADE performance ­REQUIREMENTS Owing to the complexity of the layered construction and the basic loads of the inner and outer systems, the suspended components are subject to exacting performance requirements. STRUCTURAL SYSTEM Suspended facades are exposed to various loads: – wind load (pos. and neg. pressure – horizontally) – snow loads in the case of non-vertical facades (acting vertically, and on a sloping structure also horizontally) – imposed loads (preventing falls – horizontally) – restraint loads (from changes in shape due to thermal expansion and sources of shrinkage – multidirectional) – impact loads (vehicles, intrusion – horizontally) A suspended facade is differentiated into the secondary system (mullions, transoms, frames, glazing bars) and the tertiary system (supported infill panels or cladding). When exposed to loads, facades are ­subject to deformation at their bearing, i.e. elastic deformation (deflection) and plastic deformation (creep), in ­addition to which there may be restraint loads (due to thermal expansion / contraction, or swelling / shrinkage). Where deformation is restricted, this results in stress. Such stress must not exceed the strength of the building components which must be separated by expansion joints. The primary loadbearing system is often built with greater production tolerances than the facade components. Jointed facade anchors (bearings) that allow a degree of movement can prevent the facade being affected by loads produced by changes in the primary structure. Rigid bearings in the element can help to restrict deformation of the facade, but this requires material of adequate strength and ­thickness. Thermal insulation When the suspended facade also fulfils the thermal ­insulation function of a building envelope, the following aspects have to be taken into account: – avoiding or minimising thermal bridges – limiting transmission heat loss by using components with high thermal resistance (insulation, insulating glazing) – avoiding heat loss through air exchange by using airtight construction systems on the inside and windproof connections on the outside, e.g. by applying continuous pressure on sealing profiles. It is important to ensure that the facade has sufficient thermal resistance to maintain comfortable indoor temperatures. Large glazed areas in particular permit extensive thermal radiation loss on cold days and nights, and can therefore be perceived as uncomfortably cool. Their inside surface cools down the adjacent air and causes

draughts. If adequate thermal resistance cannot be provided, temporary insulation (e.g. roller shutters in front of glazing panels) and convective heating of the external wall (radiators, floor convectors) are ­required. Solar heat gain during the heating period, by ­using glazing or transparent thermal insulation, is just as good for the overall energy balance as the reduction of thermal gain outside the heating period by using solar screening. protection against dIFFUSION AND ­CONDENSATION Joints between facade elements must be airtight, which can be achieved by applying pressure with the glazing bars on the sealing profiles (which must have sufficient deformation capacity) and by keeping the deflection of the assembly under wind load to an acceptable level. Components that are externally airtight prevent penetration by cold air and hence condensation in the building fabric, as well as penetration by rainwater or driving snow. When the entire building component is airtight, it prevents the loss of warm air to the outside due to negative wind pressure and hence heat loss. Components that are sealed against the ingress of water (under pressure) protect the fabric from driving rain. Where external skins and joints are designed not to be watertight, any penetrating water enters an air gap from where it is conducted back outside; the gap should be pressure-equalised to render any flow of air insignificant. Special openings are provided to ensure pressure equalisation and water discharge. The inside face of an external wall should be kept warm enough to avoid condensation at the surface and thus mould growth. Where the construction makes this impossible, condensate channels are provided to control the discharge of water. The seals of glazing panels and window casements cannot always prevent the penetration of humid air. The resulting condensate collects in rebates or profiles and is led outside. FIRE AND lightning PROTECTION The fire safety concept must include the facade. In some classes of building, if there is a risk of flashover via the facade, this must have adequate fire-resistance (E30 to E90) and residual stability. This should be settled early in the design stage as it limits the choice of structure and material. Alternatively, flashover can be hindered by using non-combustible components in the facade (e.g. canopies or horizontal ledges, projecting walls, or wall panels beneath windows in a material such as reinforced concrete. These influence the transparency or opacity of the design. Connections and fastening devices attached to the loadbearing system must be non-combustible. Falling facade elements should not pose a threat to rescuers and occupants in a fire.

66  NON SELF-SUPPORTING ENVELOPES

M U L LION / T R ANSOM FACADE

The curtain wall principle gained ground internationally in the 1960s owing to the maximum transparency of this type of facade and its technical possibilities. The separation of the loadbearing structure from the envelope, and the desire for an apparently seamless transition ­between the interior and exterior (as designed in buildings by SOM Skidmore Owings Merrill, HPP HentrichPetschnigg & Partner, and earlier by Egon Eiermann) ­encouraged the development of slender construction profiles that made it possible to enclose interiors with glass elements only. Today, slender glass facades are a firm part of the repertoire of contemporary architecture, and are being continually developed with respect to ­material properties, energy efficiency and sustainability. The most common facade system is the mullion / transom construction system. The principle of separating the load of the facade from the primary structure of the building by using a secondary structure consisting of mullions, transoms and infill panels allows great freedom in the design of the facade, as this can be structured ­flexibly and independently of the building layout, including solar screening and services. The pronounced grid pattern of the exterior envelope imposed by the visible secondary structure needs special attention in terms of conceptual and detailed ­design.  p. 20 Economic solutions are facilitated by the availability of comparatively large infill elements of varying widths, profiles of varying dimensions, a range of ­different construction ­materials (e.g. steel, aluminium or timber profiles) and modular construction. Installation on site is carried out either with prefabricated ­elements or with the individual facade components. Mullion / transom systems can be used in vertical and sloping facades, as well as in roof ­construction.

Construction ELEMENTS The construction consists of vertical mullions that are attached to the primary loadbearing structure. They are commonly either supported on or suspended from the edges of the floor slabs, thereby transferring the dead loads and any loads from positive or negative wind pressure. Horizontal transoms connect the vertical loadtransferring mullions, to which they are fixed either with 1a bolts, by welding or using a push-fit system. In order to be able to withstand wind load, mullions and transoms must have an adequate resistance moment, which is why they often consist of rectangular box sections with appropriate depth. These sections may consist of coated steel, stainless steel or anodised aluminium, and more rarely of timber, veneered plywood or plastic. Steel profiles are always used to reinforce plastic profiles and sometimes, in the case of greater loads, to reinforce aluminium profiles. Metal and plastic facades work with profile widths of ­between 50 and 60 mm and profile depths of between b 50 and 190 mm; where a greater depth is required, a 1 Profile schematics frame profile is bolted onto a rectangular hollow section. It is common to use the vertical mullions for the transfer a Aluminium profile with thermal of loads, which is why they carry more weight and have a separation b Timber section with thermal greater depth than the horizontal transoms. For exam- ­separation and system profile ple, they are attached to the floor slabs or structural beams/lintels with a fastening method designed to resist tensile stress. The spacing of mullions is usually between 60 and 150 cm and is aligned with the dimensions of the fitting out grid. The facade anchors must be capable of absorbing tolerances and deformation, and must be ­designed to accommodate any thermal expansion of the secondary structure.  4

2 AachenMünchner Versicherung, Aachen, 2010, kadawittfeld­ architektur: The facade facing the boulevard connects the main entrance with the different, staggered, building volumes via a slender storey-height mullion / transom construction with structural glazing. The 2.70 m grid with two layers of insulating glazing and some curved glass panes provides maximum transparency.

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3 The Folkwang Library in Essen, 2014, Max Dudler: Light is a sen­ sitive issue in library buildings and ­requires detailed attention. Direct intensive light must be avoided. The insulating glazing unit of a conventional mullion /transom facade is given a ­polychromatic photographic imprint on the side.

MULLION /  T RANSOM FACADE  67

4 Schematic structure of a ­mullion / transom facade b

a Primary structure – floor slab, columns etc. b Facade mullion – vertical c Mullion holders d Facade transom – horizontal e Infill unit transparent, e.g. fixed glazing or opening unit opaque, e.g. solid panel f Glare / solar screening g Pressure plate and screws

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5 Comparison of historic and ­contemporary facade details a The Seagram Building, New York, 1958, Ludwig Mies van der Rohe and Philip Johnson Horizontal section, scale 1:5 b Present-day mullion / transom ­facade: additional requirements have led to ever more complex ­designs. Horizontal section through mullion, scale 1:5

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68  NON SELF-SUPPORTING ENVELOPES

infill panels Infill panels may consist of a range of different materials, be they transparent or opaque. If infill panels of different thicknesses are used, the difference can usually be accommodated by the skeleton construction system. As well as insulating glazing, common infill elements are ­panels with a covering layer of metal, plastic or (enamelled) glass, and a core of mineral wool or polyurethane foam. Various opening elements can be integrated in all systems. Vertical and horizontal pressure plates that hold the infill elements are attached to the framing and exert even, linear pressure on the infill elements and the ­substructure. Elastic sealing profiles (made of neoprene, ethylene propylene diene monomer (EPDM), PVC containing plasticiser) or silicone are inserted in the joints of the ­infill elements with the mullions / transoms and the pressure plates, and held fixed. This means that the construction consists of two sealing planes – the external cladding layer is watertight and the inner layer is vapourproof. If the size of the infill element is not large enough to close the opening of the shell construction – i.e. several elements are needed with a joint – or it has limited structural capability, horizontal transoms (bars) have to be inserted to ensure adequate stiffness and to transfer the weight to the vertical mullions. The use of transoms prevents movement due to thermal expansion, which means that expansion joints are required; these may show in the ­elevation of the facade and therefore need to be taken into consideration in the design. DESIGN CONSIDERATIONS Infill elements consisting of insulating glazing or panels represent the actual building envelope and have a major impact on the appearance. This envelope provides airtightness, wind protection, sound insulation, protection against driving rain, and thermal insulation. In the design of the joints, the following need to be taken into account: – Thermal separation Thermal separation is achieved by inserting plastic strips or profiles into the metal profiles, or by separating the construction to form an inner loadbearing skin and an outer pressure plate, whereby the insulating layer is only penetrated where the bolts are fitted; it is also possible to screw the bolts into a plastic profile. The heat flow at the screw-in points should be minimised in any case. – Resistance to driving rain and condensate Due to unavoidable geometric failure points in the seals, it is possible that humid air from the inside and driving rain from the outside penetrate the joint. Any condensate and rainwater must be collected in the profile and conducted to the outside in a controlled way; water vapour

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is discharged by ventilation (double joint seal), as otherwise there would be positive vapour pressure in the profile and vapour could penetrate into glazing and other panels via the edge seal. b

Several systems are available for sealing the joints and fastening the infill panels: – Glazing putty Owing to its adhesive and cohesive properties, putty is waterproof and malleable, but it tends to become brittle when exposed to UV light, so it has to be protected with a coating. These days it is only used for the refurbishment of historic building components. – Pressure plates with sealing profiles The most common system for mullion/transom facades uses a pressure plate that is screwed either into the frame profile or into a thermally separating plastic batten mounted on the outside. This batten presses on inserted rubber seals and is protected against the weather by a clipped-on covering strip. The covering strip can have various shapes, depending on the design intention. – Structural glazing In order to achieve a flush appearance in glass facades with as little of the profiles’ surface showing as possible, ‘structural glazing’ facades have been developed, in which glass panes are held in place by structural sealant rather than mechanically. In such systems the glass panes are not clamped against the substructure, but are held with adhesive sealant. In Germany, it is a legal requirement for these glass panes also to be secured with concealed screw connections. The external joints are approx. 20 mm wide and are sealed with a permanently elastic compound. The adhesive bond is designed to transfer wind forces only; the dead weight of the structure is transferred by fixing the glazing to small brackets or pads in order to ensure that, in the case of failure of the adhesive bond the glass panes cannot fall down (particularly important with high buildings).

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3 1 Principle of opening element connection a Horizontal section b Vertical section 2 Different types of pressure plate Pressure plates transfer forces ­between the frame and the infill panels; these plates come in a ­variety of depths and shapes, and ­cover the construction. 3 Principle of structural glazing

MULLION /  T RANSOM FACADE  69

4 Load transfer in a curtain wall ­facade The facade components can either be suspended from the top or built up from the bottom. When they are suspended (fixed at the top), the components of the facade are subject to tensile stress from their own weight, while components built up from the bottom (standing) are ­subject to compression stress and have to be secured against buckling. For this reason, facades suspended from the top can be ­designed with slenderer profiles. a Standing b Suspended 5 Salewa headquarters, Bolzano, 2012, Cino Zucchi + Park associati Imposing all-glass facade using a structural glazing system. A continuous surface is created on the outside by using profiles that can only be seen on the inside; on the outside only the glass surfaces with slender shadow joints are visible.

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6 Schematic connection to ­primary structure, scale 1:20 a Mullion profile b Transom profile c Adjustable connection at the top with height adjustment d Fixed connection at base e Insulating glazing unit f Insulation panel and seal of joint with the floor slab

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70  NON SELF-SUPPORTING ENVELOPES

GL ASS AND GL A ZING EL EMEN TS

Glass is neither combustible nor flammable; it is transparent, has a homogeneous, smooth surface that can easily be cleaned and is resistant to chemical reactions. Glass is water-repellent and does not change its shape when exposed to fluctuations in temperature. Glass has high compressive strength, but low tensile strength. The infill panels in mullion/transom construction systems may consist of insulating glazing elements, optionally filled with transparent thermal insulation or light-diffusion inserts. Element facades or double-skin facades may also feature back ventilation; this makes it possible to install photovoltaic (PV) elements, solar thermal panels or printed/enamelled glass panels, at the back of which very high temperatures may occur. The desire for a glass construction system that functions not only as bracing, but also as a primary structure, is reflected in architectural designs of great transparency and lightness, which appropriately display the special characteristics of glass. This development has led to a number of modern glass construction systems that transfer their dead weight via glass columns, glass beams and glass fins. This has become possible owing to the optimisation of the material properties of glass for structural applications, for example by using semi-tempered glass panels or laminated safety glass for transferring loads within the plane of the glass. For reasons of safety and loadbearing capacity, glass facades are often constructed using laminated safety glass. This is produced using toughened safety glass and semi-tempered glass, which are bonded together in several layers including elastic tear-resistant polymer films. Should the glass fracture, the fragments are held in place by the film. Today, some types of laminated glass that are bonded using casting resin are also classed as laminated safety glass for the purpose of building control approval.

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FASTENING METHODS A range of different systems can be used for fastening glass panes and transferring the loads: – Fastening using pressure plates In a construction with pressure plates, the loads in the plane of the glass panes are transferred to brackets at the lower edge of the glass. Pressure plates with elastic padding absorb the loads perpendicular to the glass panes. In addition, the lateral and top edges are secured with pressure plates to prevent deformation. The unrestrained corners of the glass are free of stress.  4 – Bearing on pins In this system, panes of laminated safety glass are supported from steel brackets, with the panes overlapping like scales. Owing to the system’s poor resistance to 3a

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­ riving rain, it is only used for back-ventilated or lowd specification facades, depending on the use and function of the building. While the glass panes are supported by brackets (pins) at the bottom, at the top edge they lean inwards and are held by the bearings; the bottom support is not continuous but at points. Where wind forces have to be taken into account, laminated safety glass (3 × TSG) is required. Wind forces are transferred through friction or by counter-bearings. The edges of the glass panes are completely free of stress.  5 – Disc fastening system This system is suitable for insulation glazing; the edges of the glass panels are free of stress. In a pre-stressed fastening system with discs, a hole is inserted at precise points and a polymer bushing is inserted, through which the anchor bolt is pushed. This avoids tension peaks due to imperfections. Conical pressure plates (countersink holders) can also be fitted flush with the surface. The load transfer can take place by pre-tensioning the seal and glass pane via the bolt fixing through friction and through shear stress at the flank of the hole. Alternatively, it is possible to use undercut anchors; however, this system results in very high stresses around the hole.

1 Office building, Zamora, 2012, Alberto Campo Baeza: The continuous two-layer envelope made of laminated safety glass panes with a horizontal glass edge to the roof is joined with silicone joints and rails recessed in the ground. Laminated safety glass fins provide rigidity to the joints of the glass panels on the upper floor. 2 Herz Jesu church, Munich, 2000, Allmann Sattler Wappner ­Architects: Core elements of the glass facade are the horizontal and vertical glass fins, which perform a loadbearing function and have been bonded to U-shaped stainless steel profiles for the transfer of loads. Extensive experimental and theoretical investigation was required to furnish proof of the loadbearing capacity.

3 Breaking patterns of glass Thermally pre-stressed glass panes are classified either as semi-tempered glass or toughened safety glass. The latter crumbles into small, almost spherical parts, while the former breaks into large radial shards. Semi-tempered glass is used where the broken shards will remain in the frame or cannot fall out (to avoid injury).

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a Toughened safety glass b Semi-tempered glass

GLASS AND GLAZING ELEMENTS  71

4 Kattendijkdok Westkaai, ­residential towers, Belgium, 2009, ­Diener & Diener Architects: The load of the structural facade glazing in the direction of the pane (‘in plane’) is transferred to brackets using pressure plates at the lower edge of the glass. Pressure plates with elastic padding transfer any loads that are perpendicular to the pane (‘out of plane’). In addition, the lateral and top edges are secured with pressure plates to prevent ­deformation. This means that the free corners of the glass are free of stress. 5 Kunsthaus Bregenz, 1997, ­Peter Zumthor: Laminated safety glass is supported by steel brackets at various points at the base. Where the glass panes are supported by pins, they slant inwards at the top edge against the bearing. They overlap in the manner of scales. Wind forces are transferred through friction, which requires heavy glass panes made of laminated safety glass (3 × toughened glass), or by counter-bearings. The edges of the glass panes are completely free of tension. Owing to its poor resistance to driving rain, this system can only be used for back-ventilated facades or those with low weatherproofing requirements. 6 Stadttor Düsseldorf, 1997, Overdieck Petzinka and Partners: Corridor facade with external ­single-glazing anchored at points. The pre-stressed fastening system with discs requires drill holes that are precisely positioned and tailored for the insertion of polymer bushings through which the anchor bolt is pushed. This avoids tension peaks due to imperfections. Conical pressure plates (countersink holders) can also be fitted flush with the surface. For the purpose of fastening glass panes in holes subject to shear at the reveals, the screw is cast in plastic in the hole in order to ensure an even transfer of forces. 7 Helsinki Music Hall, 2011, ­Laiho-Pulkkinen-Raunio Architects: For the purpose of reinforcement, glass fins are attached to the ­facade using point anchors and bonding.

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– Point fastening using bolts These point fastenings result in local stress peaks in the glass with high loads, which is why the preferred method is to use drilled point fastening devices. The means of transferring loads from the glass pane to the secondary loadbearing system must be capable of accommodating thermal and wind-related deformation. This is achieved by having one fixed point and three anchor points that ­allow movement. Systems that use point fastening methods require laminated safety glass or semi-tempered glass, because if  one pane fails, the adjacent panes or other building components have to absorb the resulting forces. Glass beams (glass fins) and also glass needles can be used to provide stiffness against negative wind pressure. Joints are sealed with a permanently elastic compound. Where insulating glass panels are used, an additional inner rubber profile helps to equalise vapour pressure and discharge water. In the case of insulation glazing without a frame, a means of draining water from the rebate joint must be provided, the sealing system must have sufficient mechanical strength and the edge seal must be ­UV-resistant.  6 – Fastening system using adhesive bonding It is also possible to bond holding discs to the glass using elastic adhesive; this bond is capable of absorbing small rotational movements. A separate construction is required to prevent glass panes from falling should any of the holding discs fail.  7

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SECONDARY LOADBEARING SYSTEMS Glazing with point fastening systems can either be supported by a range of loadbearing systems or it can be part of a secondary system. The following secondary loadbearing systems are available: – Frame systems consisting of profile tubes These consist of a number of profile tubes that are joined to form a grid frame similar to a mullion / transom system. Frame systems are very stiff, so any deformation has to be accommodated by the anchor fastenings. – Cable networks Flat or curved space frames consist of cables with compression struts inserted between them. This system ­requires two cable systems, one for negative and one for positive wind pressure. In spite of the pre-tensioning, ­significant deformation takes place. – Vertical cable facades These consist of vertical cables or tensile bars suspended from the top, allowing a very slender loadbearing system. The pane fastenings are attached to the cables and transfer the weight of the glass and wind forces. One version of this system is the glass curtain in which the glass panes – utilising pre-tensioning – make up the tensile elements. The glass panes are attached at four points. This type of glass element facade is highly complex and requires cooperation with consulting engineers early in the design stage. Designs using this system do not readily fall into any standard structural category and therefore usually require individual consent from the building control authorities, unless the necessary evidence of structural integrity is available for an approved system.

72  NON SELF-SUPPORTING ENVELOPES

EL EMEN T FACADE

Element facades consist of storey-high elements forming complete room enclosures. They are an efficient ­alternative to a classic mullion / transom construction in situations where a homogeneous facade surface, such as that of a tower block, has to be installed without scaffolding in a short period of time, or where a facade has to be installed in a restricted space as part of a revita­ lisation project. Each module contains the necessary components of a building envelope, including the rigid loadbearing frames, transparent glazing (either fixed or openable), opaque panels, ventilation elements and the part covering the edge of floor slabs, in the form of a single- or double-skin system. In contrast to conventional mullion / transom construction, prefabrication allows the profiles of the opening elements to be slimmer, which means that the visible profile width is reduced. In addition, prefabrication at the factory means that solar screening elements can also be fitted. The functional requirements for the building envelope affect the design of the facade. Depending on the way in which opening and ventilation elements are integrated (full-panel size / with a separate frame in the centre of the element / in small-format horizontal bands / alternating with closed elements), the design of the facade varies, resulting in different aesthetic effects. The jointing of prefabricated elements on site involves extensive logistics and requires exact detailing of the design of the construction and expansion joints; an important aspect of this facade system is the fact that the shell construction has to be completed to minimal tolerances.

Installation The individual elements are installed storey by storey in front of the shell construction plane using precisely aligned fixing plates, either fixed rigidly or with a movement tolerance, and are aligned in all three dimensions within the available tolerances. Following the installation of the facade, the interior fit-out can start without any delay. The usual width of the prefabricated elements ranges from approx. 120 cm to 250 cm, the elements being manufactured to suit the axes of the grid system. Lightweight timber constructions can be produced covering several axes, up to a width of 6 m; narrow metal panels can be produced up to 14 m long. If the elements are taller than the full-storey height, they have to be transported flat (up to 250 cm wide) owing to road transport regulations. Prior to installation they have to be erected by crane. As individual elements are installed side by side, the visible width of the edge profiles is combined. The standard width of the mullion (twice the edge width of a single element) is approx. 80 mm. The covering function can be performed by a pressure plate (which is also preassembled in two half shells) or by the detailing of the structural glazing system. sealing The elements are joined using special overlapping connection joints – horizontally with continuous sealing rails and vertically with push-fit seals. A distinction is made between, on the one hand, the joints within the element which, similar to those in the mullion / transom facade, are

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1, 4  Office building, Münster, 2011, Vervoorts & Schindler ­Architects: The facade elements were prefabricated and inserted as functional units. The solar screening has been integrated in the elements to create a flush ­surface, thus retaining a harmonious exterior when the screening is closed. 2 The connection points of the ­facade to the primary system must have fixed points as well as sliding ones, which must be three-dimensionally adjustable so that tolerances in the construction can be ­accommodated. 3 Schematic of element facade a Floor slab b Facade element c Element connector d Glazing

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5 The Prime Tower, Zurich, 2011, Gigon Guyer: Elements such as the automatically operated large parallel opening windows of up to 400 kg are integrated in the ­element facade.

sealed using permanently elastic compound or pre-compressed sealing strips, and on the other hand, the joints between the elements. The latter are closed with pressure plate seals unless the geometry of the joint and the installation sequence make it possible to insert the seal during installation. The joints between the elements must be capable of absorbing all of the thermal deformation of the components which, due to the larger size of the elements, is greater than that of mullion / transom elements. Constructions with elements fastened in this way can be installed to a facade length of 50 m and still absorb the resulting ­expansion in the joints. In spite of the ability to absorb deformation, the joint between the elements must remain watertight and airtight. The selection of the panel material and the design of the profiles have to take into ­account building physics requirements for the facade, such as thermal and sound insulation, fire protection and effective solar screening independent of the weather, as well as safety requirements. The most commonly used profiles consist of extruded aluminium sections with thermal separation; however, it is also possible to produce special profiles from a variety of materials, such as structural bronze.

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6 Schematic facade section, scale 1:20 a Floor slab b Facade element c Element holder with fixed and sliding points d Element connection

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74  NON SELF-SUPPORTING ENVELOPES

D O UB L E-SKIN FACADE

The principle of the double-skin facade (as opposed to the single-skin element facade) is based on a development of the historical box-type window in which, sometimes seasonally, a secondary window is fitted in order to achieve a climate buffer between the two. Today, doubleskin facades consist of two planes – an outer glazed skin which protects against the weather, and an inner thermally insulating construction plane which can be configured to suit the various functional requirements (solar screening, protection against glare, thermal and sound insulation, natural ventilation and provision of daylight). Between the two skins is an air-filled space that functions as a thermal buffer zone. One of the objectives in the development of this facade system was to achieve natural ventilation of the interior, rather than having to use air conditioning, and thus to improve the quality of the interior climate. The space between the two skins can be ­accessed via ventilation openings, installed either in the outer or the inner skin – a solution that is also possible in very tall buildings. Another advantage is that solar irradiation can be utilised for seasonal heat storage and natural thermal convection in order to encourage a steady flow of air. Double-skinned facades, appropriately designed to meet structural building physics requirements, can be particularly suitable for tall buildings exposed to strong wind loads and requiring extensive sound insulation. However, in view of the additional cost of a double-skin facade, designers may want to consider whether it is necessary on all sides of the building. Where double-skin facades are used on two sides of the building only, special attention must be paid to the transition between the different types of facade construction. A distinction is made between different types of double-skin facade, depending on the different types of ­ventilation. MECHANICALLY VENTILATED FACADES These facades consist of a closed external envelope of insulating glazing and an internal facade of single glazing, which can be opened for the purpose of cleaning and  maintenance. The difference to other systems is the mechanical air movement, in which warm preconditioned air is directed through the air space and discharged above the roof. An advantage of this system is the good sound insulation, while the energy consumed is a negative ­aspect. SECOND-SKIN FACADES In this system, a lightweight second layer without horizontal or vertical compartmentalisation is placed in front of the actual facade, enveloping the entire building and creating a layer of air as a buffer in front of the facade.

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This buffer zone is also used for ventilation. In winter, this zone can be closed to the outside and used for storing solar irradiation, while in summer the openings in the outer layer can be opened to prevent overheating. The intermediate space of the buffer zone may be quite narrow, or it may have considerable depth, thus creating a new, enclosed space of its own. An advantage is good ­external sound insulation; a disadvantage is the transfer of sound within the building via the surrounding air space. A development of this system is the closed cavity facade (CCF), in which the space between the inner and outer facade skins is lightly pressurised and fully encapsulated. Dry, clean air is injected, which prevents the formation of condensate and soiling. The cavity can accommodate ­solar screening and light-directing elements. In contrast to the mechanically ventilated facade, the second-skin ­facade relies on natural thermal convection. CORRIDOR FACADE AND SHAFT BOX FACADE Another variant is the corridor facade, in which the air is injected separately for each storey. The inlet and outlet air openings are arranged in an offset manner in order to prevent any thermal overlay of the air flow. The resulting corridor is also used as a cleaning platform. An advantage is that each storey is individually protected against overheating. The construction of the shaft box facade (a further variant) is based on alternating box-type windows with ventilation shafts. Owing to the stack ­effect, air is sucked into the shafts at low level, heats up and flows past the box openings, thereby providing a comfortable room climate. Due to the low proportion of openings, the sound insulation of this facade is good. However, the natural stack effect decreases with increasing height, so that this type of facade is unsuitable for tall buildings.

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1 Schematics of double-skin ­facades a Facade with second skin b Corridor facade c Shaft box type facade

DOUBLE-SKIN FACADE  75

2 Süddeutscher Verlag tower, ­Munich, 2008, GKK+Architekten Prof. Swantje Kühn, Oliver Kühn: According to calculations by the ­architects and engineers, the building is expected to save 80 % of the primary energy that would normally be used during operation, and hence reduce operating costs by up to 35 % compared to comparable conventional buildings. This result is due to the double-skin facades with decentralised facade ventilation devices, the individual control of ventilation, solar screening and temperature in each office, and the use of the ground storage systems for heating / cooling according to the season.

2 3 Allianz headquarters, Zurich, 2014, Wiel Arets Architects A development of the ‘closed cavity’ facade, with self-contained, highly insulating box-type window elements, the cavity of which is used for conducting dried air. In contrast to double-skin facades with openings to the outside air, this system prevents the ingress of dirt or dust into the box element and also prevents condensate forming in the ­facade gap. This means that the glass surfaces facing the gap do not have to be cleaned. Curtains with a highly reflective aluminium coating are used as integrated ­solar and glare screening.

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76  NON SELF-SUPPORTING ENVELOPES

EL EMENT FACADE – CONCRE T E

1 Suspended prefabricated components are subject to tensile stress only, which affects the type of reinforcement. For this reason they usually only suffer shrinkage cracks, and transfer all impacting forces to the primary system, which must be capable of absorbing them.

Element facades made of concrete consist of individual prefabricated elements that are installed and joined on the construction site, forming a secondary structural system. They are distinct from single- and multi-skin prefabricated concrete units which, like sandwich construction units, form part of the primary structural system. Prefabricated concrete elements consist of several layers: the loadbearing layer, a thermal insulation layer and a face layer. It is also possible to include an air gap in the construction of the elements. The large-format prefabricated elements – which consist of reinforced concrete or lightweight concrete with a dense structure – can be produced up to a length of approx. 5 to 6 m to cover the full height of a storey. The size of elements is limited by their weight ( 300 kg/m2 in which the structural part consists of reinforced concrete, which is insulated with a thermal insulation layer and protected by a cladding layer. The stiffness of the system makes it possible to use the panels without framing. The shear-resistant bonding enables them to transfer wind forces and self-weight, and limits the deformation of the cladding skin, which would cause stresses in both layers. This means that the bonding must be flexible enough to ensure that the covering skin only suffers cracks – if any – in the micron range, otherwise driving rain can penetrate and the panels will not be frost-proof. Although metal skins are impermeable to vapour and are waterproof inside and out, water vapour can nevertheless penetrate via the thicker inner concrete layer and it must be possible for this to be discharged to the outside. For this reason, the thermal insulation must be resistant to damage from moisture. The junctions between the elements themselves are sealed with double joint sealers in all systems. An air-tight inner tape limits the ingress of water vapour and humid air, and an outer drainage chamber with appropriate joint geometry, or an air-tight diffusive outer seal, ensures that any water can drain off and that the joint is continually vented. Sandwich elements are usually storey-high and are placed into the openings of the primary structure. This means that both the insulation and the covering skin can be contin-

1 1 Olympic Village, Munich, 1972, 2010 Werner Wirsing, bogevischs buero: Instead of refurbishment, it was decided to rebuild the student housing (1,052 terraced houses in miniature format) in the former Olympic Village in sandwich construction. The original project had been built from prefabricated concrete units.

uous in front of the primary system and thermal bridges can be avoided. The geometry of the projecting covering skin determines the position of the element joints. The elements’ own weight is transferred via the structural layer while horizontal forces are transferred via more substantial connections than usual or via anchoring to the intermediate floors of the building. The functionality of the system depends on the careful detailing of the joints – both inside and out. Elements into which moisture has penetrated must be replaced. CONCRETE SANDWICH ELEMENTS As a rule, concrete sandwich elements consist of standard reinforced concrete. In order to minimise the work of installation, elements are usually storey-high and approx. 5 to 6 m long. From the point of view of cost-effectiveness, one should consider that small elements mean more joints and are therefore more costly to produce, whereas large elements require a stronger primary structure. Since the inner layer consists of concrete approx. 15 to 20 cm thick, it can provide good fire protection (fire resistance of 90 minutes); in addition, the substantial thermal mass of the material helps to reduce overheating in summer. The covering layer stores part of the ambient heat and thereby reduces the amount of thermal radiation reaching the interior. The stresses and deformations resulting from changes in temperature must be absorbed in the joints between the elements. In the exterior layer, the reinforcement should be covered by concrete of a depth that is sufficient with regard to the texture of the surface and the harshness of the ­environment.

2 With concrete sandwich elements, the loadbearing layer must be at least twice as thick as the 7–10 cm thick covering layer in order to be able to absorb the quantity of water vapour that penetrates through diffusion and to allow the element to dry out sufficiently. The connection between the layers relies on (stainless) steel thrust ­anchors; the insulation must be pressure and moisture resistant, the usual choice is expanded polystyrene.

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3 Cloth factory, Berlin, 2014, nps tchoban voss: The building ­envelope was to be refurbished, but the existing structural fabric could only support minor additional loads. By using lightweight, extremely smooth aluminium sandwich elements with high structural strength, the weight of the new facade was kept to a minimum. The design of the facade pays homage to cloth as a material, as the panelling has been printed with a pattern that runs around the building like thread on a weaving loom. 4 The layers of metal sandwich ­elements (metal panels) are bonded to create a shear-resistant connection. The polyurethane foam that is applied as thermal insulation also 3 bonds directly with the metal. Any mineral wool insulation needed for fire resistance is attached with adhesive. The rigidity of the system is limited by the strength of the ­insulation. 5 Schematic section through ­metal panel a Horizontal b Vertical

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6 Schematic section through ­ oncrete sandwich element c a Horizontal b Vertical aa  Loadbearing layer bb  Thermal insulation cc  Joint dd Grouting ee  Sealing tape, sealing profile

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Metal panels Metal sandwich elements are lighter in weight and are used for large spans in order to save material and reduce load. Metal panels are usually produced from strip galvanised steel sheeting with a coloured coating; occasionally also from aluminium or stainless steel. The elements are 60 to 100 cm wide and up to approx. 14 m long, which determines the number of joints. In ­order to improve the stiffness of the panels, it is possible to use metal sheeting with profiling in the longitudinal direction. Metal panels are attached to the loadbearing structure using metal brackets that are part of the system. The fixing distance depends on the prevailing wind forces and the resistance moment of the panels. In order to prevent damage to the thin fixing sheets or panel sheets when exposed to the suction force of wind, the size of the elements or the spacing of fixings is adjusted appropriately. Any projecting building component such as parapet panels requires a bracing substructure. To protect the elements from the ingress of moisture, the two meeting edges along the longitudinal joint are profiled, while the lateral joint is butted. Similar to internal and external corners, lateral joints should be covered with profiled metal sheet sections, for example; they are also prone to deformation and require a stiff substructure. Windows and other infill components are attached to the substructure and not to the panels, so they have to be connected with sufficient tolerance while ensuring airtightness and providing protection against driving rain. When selecting the covering layer and insulation material, as well as the type of bonding and connection joint, the required fire resistance class must be taken into ­account. A special feature of metal panels is plastic ­deformation of the metal, which creates a camber for greater stiffness, for example in the case of different internal and external temperatures, owing to the greater longitudinal expansion on the warm side. This effect can be detected in glancing light. The deformation must be taken into ­account when designing the connection details. Owing to their rapid installation, relatively low weight and standardised fixing details, metal sandwich facades are a cost-effective solution, especially when the elements can be attached directly to the primary system. The placing of joints and windows – in particular, the detail of the lateral joints – has an effect on the design and the structural system, and must be carefully considered.

82  NON SELF-SUPPORTING ENVELOPES

SUSPENDED FACADE – FACE B RICK WORK

In their appearance, outside layers consisting of face brickwork are similar to solid brickwork. Traditional double-skin construction – which has the purpose of combining the different qualities of masonry, i.e. water-resistant clinker bricks as weather protection and masonry units as a loadbearing layer – has been developed further to meet increased requirements regarding thermal insulation and weather protection, and is widely used in ­regions where brick construction is a traditional feature. As with face brickwork, special requirements apply to the design of the exterior surface and the joint pattern. Never­theless, face brickwork too opens up a wide range of design options. The space between the outer and inner layers can be used to integrate sliding elements, window frames, and light fittings. The material of the facade can consist of masonry units with different colours, which can be arranged to form patterns similar to marquetry work. Likewise, it is possible to create differences in depth to provide a more pronounced texture to a facade. Face brickwork is part of a two-skin system in which the other skin consists of masonry or reinforced concrete. This inner skin provides an impervious closure and transfers the vertical and horizontal loads. The outer skin (face brickwork) determines the visual appearance and provides protection against the weather. In order to ensure adequate back ventilation, the minimum distance between the two skins must be 40 mm, while the maximum distance must not exceed 200 mm. A basic distinction is made between: double-skin external walls with an air gap; double-skin external walls with an air gap and thermal insulation; double-skin external walls with core insulation, and double-skin external walls with a coating of render as a barrier layer (detail for exceptional cases).  2

Material Brick is the summary term for single masonry units consisting of clay, sand and lime, or a concrete material that are hardened by a firing or air-drying process. Bricks for brick cladding are used as protection against the weather and therefore have to meet certain requirements which are specified in DIN EN 771-1 and DIN V 105-100, one of them being frost resistance. The standards include the following definitions: – Face bricks are high-density (HD) bricks produced industrially in various textures and colours, either as solid bricks or with perforations. – Hand-formed bricks are produced without perforations and feature an heterogeneous surface. – Clinker bricks are HD bricks fired at high temperatures so that the surface sinters: melting the material and forming a vitreous, glazed finish. – Ceramic clinker bricks are HD bricks formed from highquality clay that, in the firing process, sinters into a high-density material. Special bricks are manufactured in various shapes to produce specific design effects for facades or other building components. The colour and surface texture of face bricks can be ­affected by the chemical reaction of the components contained in the raw material and by changes of temperature during the firing process. An important factor that affects the colour of the material is the amount of oxygen input during the firing process, with more oxygen ­resulting in reddish shades and less oxygen in blue / black hues. In addition to the differences resulting from industrial or manual production, the texture can be varied further by mechanical processing or patterns in the moulds.

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1 1 Vertical expansion joints should be arranged at the corners of the building and – in the case of a standing cladding layer – at different levels, as well as at lintels and underneath windows. In the case of large, continuous masonry surfaces, expansion joints should be provided every 8 to 12 m, depending on the type of masonry unit. 2 Double-skin systems: a Double-skin external wall with air gap b Double-skin external wall with air gap and thermal insulation c Double-skin external wall with core insulation d Double-skin external wall with layer of render

3 Sealing at the base to DIN 1053-1

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Owing to the joints in the brickwork, face brick layers are not waterproof. This means that water draining ­details must be provided behind the face brick. In any case, the insulation used should be permanently hydrophobic.

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aa Depth of anchor penetration ≥ 50 mm bb Face brickwork cc Wire wall ties with drip disc dd Air gap ≥ 40 mm ee Loadbearing wall ff Internal plaster gg Core insulation, max. 150 mm gap hh Plaster layer ii Narrow gap (10 to 20 mm)

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SUSPENDED FACADE – FACE BRICKWORK  83

Owing to the thermal expansion of the material, it is important to include expansion joints in the construction. As a rule of thumb, expansion joints with a width of 10 to 15 mm have to be provided in brick facades at about 12 m spacing, and have to be closed with a suitable permanently elastic sealing material. The arrangement  of joints should be considered at the design stage, as they can be used to underscore the functions of the building or, conversely, be placed such that they are not very conspicuous. Openings that are arranged in strict vertical alignment make it easier to accommodate expansion joints, while meandering joints in random bond brickwork are less conspicuous.  1

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4 Steel brackets support the weight of the face brickwork and transmit it to the loadbearing structure via dowels or anchor rails cast into the concrete. The bearing plate and design of the anchor bracket can vary, depending on the load to be supported. 5 Anchors through the air gap ­secure the face brickwork against buckling and transmit any horizontal wind forces to the loadbearing structure. 6 Munich Technical University, 2012, Hild & K: The main building of the Munich Technical University was built using a reinforced concrete skeleton system in 1959. The refurbishment required a redesign of the facade, the construction of which was completed with clinker face brick. The vertical pillars are shaped in ­undulations which are vertically offset. This sculptural design is intended to express the non-loadbearing function of the wall. In view of the fact that some of these undulations project up to 700 mm from the ­facade surface, special support brackets and anchors with a greater diameter and with lengths of ­between 450 and 820 mm had to be used (standard anchors are only approved for distances of up to 200 mm). 6

construction In order to transfer the weight of the exterior skin to the loadbearing wall, it is necessary to provide brackets or support ledges, which must support the full width of the brick. Common details involve projections at intermediate floor level, or corrosion-resistant steel sections that are either dowelled to the concrete, or cast in it. Projecting continuous horizontal concrete bearings can result in a visually interesting facade structure. In order to achieve the necessary thermal insulation performance, such bearings require careful and usually complex de­ tailing.  4, 5

The vertical distance between such bearings is about 12 m for skins with a brick width of up to 11.5 cm. ­Owing to its structural strength, exterior brick cladding of this thickness has become established in practice. Brick cladding of a lesser thickness (approved thickness is ≥ 9 cm) may only installed up to a height of 20 m above ground and must be supported at 6-metre intervals. The cladding skin is connected to the loadbearing inner skin using non-rusting Z- or L-shaped wire ties to prevent any buckling or tilting. This form of anchoring is also used to transfer wind loads, whereby the anchors must be capable of withstanding both positive and negative pressure in the form of compressive and tensile forces respectively. These ties should be spaced at max. 50 cm vertically and max. 75 cm horizontally. Additional fixing points must be provided at all edges, building corners, openings and along expansion joints, as well as at the top end of the exterior cladding skin (DIN 1053-1). The construction details must be formed in a way that allows moisture to be discharged (drip edges etc.). The inner skin and intermediate floors must be sealed against moisture at the base of the gap between the two skins. Any moisture penetrating the brick cladding will thereby be conducted to the outside, away from the building. For this reason, the sealing component in the gap must be installed with a fall towards the outside.  3

84  NON SELF-SUPPORTING ENVELOPES

Above openings in the external brickwork – such as windows or doors – the wall is supported with anchor brackets or steel bearing sections. With the help of modern bearing systems, openings in brick-clad walls are easy to produce. For this reason it is also technically possible to build walls with large horizontal openings, or even fenestration bands, in contrast to traditional brickwork, in which the format of the openings is vertical, with the load from above supported by full or segmental arches. The means of supporting the load, such as lintels, can be used as a design element. In constructions with an air gap, ventilation openings must be inserted at the base and top of the cavity as well as at any intermediate bearings, in the form of open perpendicular joints. In a two-storey building with brick cladding using 52 mm thick bricks, the vents provided at the face, top and lower edges of any bearing structures should be placed at approximately ­every other perpendicular joint of the external skin.

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2 Extension to the Melanchthonhaus, Wittenberg, 2013, Dietzsch & Weber Architects: The front of the three-storey extension is aligned with the existing neighbouring buildings with the windows ­arranged at the same height as those in the Melanchthonhaus and adjoining gate building. The facade of the extension consists of stock clinker brickwork with a rough, matt surface in various shades of grey; these were was assembled on site to create the composition. The sculptural effect of the building is emphasised by recesses for the openings; the elevation appears as one monolithic element without the traditional zoning of plinth, main facade and roof. 3 Ravensburg Museum of Fine Art, 2013, Lederer Ragnarsdóttir Oei: At first sight, the new building ­appears familiar on account of its dialogue with its urban environment and the material qualities of the brick masonry. The outer skin consists of recycled bricks. The roof has been constructed of prefabricated brick vaults, which span the interior space without intermediate support. The bricks were recovered from the demolition of a Belgian monastery and, having been recycled, ­underscore the importance of sustainability in building construction.

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1 Schematic section through face brickwork, scale 1:20 a Face brickwork, 115 mm b Air gap, 40 mm c Thermal insulation, 140 mm d Loadbearing masonry, 240 mm e Steel section lintel f Wire wall tie

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SUSPENDED FACADE – BRICK PANELS  85

SUSPENDED FACADE – B RICK PANELS

4 Schematic section through brick panel facade, scale 1:20 a Brick panel, 30 mm b Panel holder c Aluminium support section, ­horizontal d Aluminium support section, ­vertical e Fixed / sliding point f Thermal insulation g Wall construction

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5 Corner details of suspended brick elements a with metal profiles b mitre cut 6 New office building, Gooiland, 2011, Koen van Velsen: The new building responds to its rural context through its traditional outline form. A geometric structure with a lightweight feel is created with the help of earth-coloured brick ­facade panels that are produced from earthenware to match the roof. The use of panels with either two or three dummy joints generates a playful surface.

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It was not possible to manufacture of brick panel faca­ des  until modern firing and production techniques had been developed. Fired and relatively large cavity panels made of clay-type material have been used for facades since the 1980s. Common formats of panels are 150 to 300 mm in width and 300 to 500 mm in length, with a thickness of approx. 30 mm. With advances in production technology, it is now possible to produce elements with a length of up to 3000 mm. In order to optimise the substructure, the panels are usually installed horizontally, although there are also vertical systems on the market. Brick cladding panels in standard formats are a cost-­ efficient alternative to face brick or natural stone faca­ des. Since this modular prefabricated material has good durability characteristics, it would appear to be suitable for facades with large surface areas, both in new construction and refurbishment work.

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CONSTRUCTION The facade system basically comprises four components: brick panels, panel holders, a horizontal support section and vertical joint profiles. The basic vertical section consists of a standard section. The brick panels are designed such that the upper panel has a nosing that overlaps the one below. The panel holders feature a clip system that allows the panels to be installed on the bearing section without using tools. Brick panels are offered in similar colours to those of roof tiles, ranging from red through to yellow and grey shades. In addition, it is possible to texture the surfaces (brushed or grooved). For larger areas, it is commercially viable to produce special solutions with respect to format and surface finish. Normally, the facades are subdivided in accordance with the selected module sizes. For this reason, the dimensions of the construction, i.e. column grids, storey heights and the dimensions of openings, should be harmonised with the size of the panels at the design stage. In the case of refurbishments, it may be opportune to vary the width of panels to compensate for different heights. In order to accommodate different lengths of panel, it is possible to cut the panels or produce them in special sizes. The corners of buildings are mastered by fixing a steel section along them, or using specially shaped panels to form a mitred corner.  5 Similarly, the details of junctions at openings, such as ­reveals and windowsills, can be resolved using metal components or specially shaped brick components. Another interesting option for the design of facades is offered by special components made of the same raw material as the brick panels, such as louvres and solar screening systems.

86  NON SELF-SUPPORTING ENVELOPES

SUSPENDED FACADE – NAT UR AL STONE

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Owing to its durability, natural stone is an obvious choice as a facade material, particularly for prestigious buildings. The characteristic pattern of the stone used and its surface finish determine the appearance of the facade. In addition, thanks to its low primary energy content, its long service life and its good recyclability, natural stone is an environmentally friendly building material. MATERIAL Natural stone is grouped by its provenance: – Igneous rock (plutonic and volcanic rock) – Sedimentary rock – Metamorphic rock The igneous rock types, such as granite and basalt, are significantly harder than sedimentary rock (sandstone and limestone). Between these two in terms of hardness are the metamorphic rocks, such as gneiss, crystalline marble and slate. Facade stone is selected for its appearance (colour and texture) and for its respective material properties, such as compressive strength, water absorption, breakout resistance, weight and thermal expansion. Differences in the rock’s colour and structure, as well as inclusions, are the result of geological processes. For this reason, and in order to take variations in texture and colour into account – as well as patination – it is important to inspect larger samples of the material when making any selection. Depending on the hardness and condition, natural stone surfaces are finished in a number of ways, including sawing, embossing, dressing, bushhammering, charring, smoothing, grinding and polishing, as well as leaving the surface unworked after quarrying.  2 These means of processing, which were originally wholly manual, can now almost all be carried out with ­machine tools. If the material is used in a uniform way at parapets, reveals, cill panels and in the plinth area, it creates an overall monolithic impression, which can be reinforced by positioning the material in one plane with

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closed joints. Open joints and mouldings or offsets in the  stone have the opposite effect and can provide a ­facade with rhythmic subdivisions or give it an animated surface texture. When designing such a facade, the maximum size of the panels must be taken into account, which depends on the type of stone and is limited by the size of blocks available. As a rule, large-format panels (upwards of approx. 1.5 m) are significantly more expensive than small ones. In addition to the higher price of the material, fitting the panels on site is more costly because large panels cannot be installed manually owing to the greater weight. The proportions of the panels are also important. For example, if panels are cut in a format in which the ratio of width to height is narrower than 1:4, there is an increased risk of breakage during transport and installation on site. In addition, the design of a facade needs to coordinate the size and arrangement of the panels with the dimensions of the openings in the facade. This involves design decisions such as whether to opt for horizontal or vertical formats, which can echo or even emphasise the shape of the building and its openings. Furthermore, details for  the connection to other building components and for the building corners have to be developed. It is also possible to accentuate certain parts of the facade, such as the plinth or the window reveals, by using a different material thickness, or a special profiling or surface texture. If the fixing points are to be provided as part of the shell construction, the facade plan needs to be produced in parallel with the detailed design of the shell construction. A common method is to produce panel position drawings as ele­vations for all facades, including the planned anchor points. Furthermore, it is important to determine the anchoring points for any scaffolding, because the anchor bushes remain in the facade so that new scaffolding can be erected without causing any damage to the structure.

3

1 House M, Grünwald, 2009, ­Titus Bernhard Architects: The back-ventilated suspended facade uses gneiss that has been sawn and broken across the strata; it has been installed with contact joints, with the rough surface facing outwards. The visible concrete floor slab has been prestressed to create a camber in order to bear the loads resulting from the cantilever. 2 a b c d e f

Surface treatments Rough hewn Brushed Picked Tooled Sandblasted Unworked

3 Carrara marble quarry

SUSPENDED FACADE – NATURAL STONE  87

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4 Anchors for natural stone a undercut anchor b anchor welding plate cast in ­concrete c dowel retaining anchor 5 Example of a facade layout plan a Panel, number and position b Anchor position with dimension details for placing the anchor pins c Indication of scaffolding anchoring points 6 Schematic section through wall with natural stone cladding, scale 1:20 a Wall construction Natural stone, 40 mm Air gap, 40 mm Insulation, 160 mm with hydrophobic treatment Reinforced concrete wall, 240 mm Internal plaster, 15 mm b Dowel retaining anchor c Roof upstand clad with natural stone, with a bonded drip d Special loadbearing brackets

CONSTRUCTION Most modern natural stone facades are installed as suspended cladding panels. In exceptional cases they can be built from the ground up instead, provided the material is thick enough.  p. 84 The structural components supporting suspended cladding usually consist of concrete, steel, or masonry. In order to connect the stone ­facade to the loadbearing structure, it is necessary to use an anchoring system or an appropriate substructure. This may consist of stainless steel, aluminium, or corrosion-protected steel. Depending on the format, the stone panels can be supported either in the horizontal joints or in the vertical. The ideal spacing of the anchors on each side is at 1/5 of the panel length from each end. Both open and closed joints are possible. When the joints are closed, the forces from negative wind pressure at the building corners and roof junctions are likely to be higher. This must be taken into account when calculating the anchor points necessary to resist wind suction factors. The structural stability of natural stone facades has to be calculated and documented in all cases. Anchors are available in the form of dowelled, welded, or mortar-embedded systems and should preferably be made of stainless steel. The selection depends on the type of substrate. In new buildings, it is possible to insert anchor bushings (or plates for attaching the anchors by welding) into the shell construction. The anchors have cylindrical bolts, which are drilled into the edges of the natural stone. For this reason, panels that are to be fitted using anchors should be at least 40 mm thick. This thickness of 40 mm is also required in order to ensure that the material is frost-proof. In existing buildings it is imperative to examine and test the substrate in which the anchors are to be fixed. Should the substrate be relatively soft, holes of a greater diameter should be bored in order to distribute the pressure of the mortar-embedded anchors over a sufficiently large area. Where the substrate is not capable of supporting the imposed loads – or where areas of insufficient loadbearing capacity have to be bridged – substructure rails can be used. These rails are also used around large openings. Special anchors are used to fix the panels at lintels and reveals. Shell constructions with thin walls ( 3 mm thickness, sheet